Black Zetsu

is half of the duo of Zetsu. An artificially created human that works in the service of Akatsuki, Black Zetsu was manifested after Madara Uchiha coated the original White Zetsu with his will. However, it was later revealed Black Zetsu is actually a manifestation of Kaguya's will, not Madara's.

Background
When Madara was on the verge of death, he manifested his will and imbued half of White Zetsu with it, thus creating Black Zetsu. This in turn made the complete Zetsu also partially a clone of Madara, albeit weaker. Both halves later accompanied Obito to Amegakure to locate Nagato, who had unknowingly been given Madara's Rinnegan as a child. Zetsu then accompanied Obito as he approached the orphans, introducing himself as Madara Uchiha.

Personality
Compared to White Zetsu, Black Zetsu, nicknamed, is more serious and knowledgeable, befitting a bearer of Madara's will. In the Japanese version of the manga, Black Zetsu only uses katakana for okurigana and furigana. This is often conveyed in the anime through a deeper voice. While he sometimes has a difference of opinions with White Zetsu, the two halves are still able to function as a single entity.

Zetsu had the skill of appearing extremely trustworthy, obedient and loyal, being entrusted with Akatsuki's secrets and knowledge of Madara's Eye of the Moon Plan. In actuality however, his true loyalties have been kept secret from nearly everyone, including Madara Uchiha himself. Because of his ties to Madara, Zetsu has been working with Obito for a long time, originally helping Obito find and convince Nagato to join them. Unlike White Zetsu, who was kind to his allies, Black Zetsu saw anyone beneath Madara as useless. When Obito lost the tailed beasts, Black Zetsu commented on how he was a more effective servant to Madara. He also had no qualms about using Obito's dying body as a host when he fought Kakashi and Minato, showing just how little he cared about the Uchiha's welfare, while deriding Obito for being useless for his treason. Despite Madara's role in his creation, his loyalties do not truly extend to him either, as he harshly betrayed him and expressed to him how he was really no different from Obito. It appears in the end, Black Zetsu's true loyalties reach only to Kaguya Ōtsutsuki, a person he claims to be the will of.

Zetsu's main role within Akatsuki is to function as a spy with other duties that were similar to those of a hunter-nin. He is also able to control his body and take part in the tailed beast sealing ritual simultaneously, which, in addition to being unique to him, allows him to act as a lookout while the sealing takes place. When an agent of Akatsuki, or possibly even a member, dies, Zetsu is sent to devour their bodies so as to not have their secrets revealed, which further adds to his nature as a half-plant creature. Zetsu is also the one sent to retrieve the rings of dead Akatsuki members. Due to the role he plays, Zetsu is the only member of Akatsuki to act without a partner on a regular basis. As such, he operated on his own, often moving between the different locations where the other Akatsuki members were located. This resulted in other members often reporting directly to him, rather than the figurehead leader, Pain. Zetsu would in turn report directly to Pain along with Obito, who took full control over the organisation after Nagato's death and treachery.

Appearance
Black Zetsu's real body is a shapeless black mass with a single eye. This mass can be resized at will, Black Zetsu also has ability to move his "eye" and consciousness to any point of the mass, even if it is being split to some parts.

Black Zetsu can cover a body of a living being and control it. When his creation was introduced, Madara infused him onto the deformed right half of White Zetsu's body, and from then on Black Zetsu used it for the most part of the manga. When together, the two Zetsu were easily distinguished by the two venus flytrap-like extensions that emerged from their sides, enveloping their head and upper body as a shell, which they were able to open and close. Beneath these extensions, Black Zetsu got usual White Zetsu's short green hair and yellow eye on his side. The black colour did not cover Black Zetsu's entire body, as it only extended partially down his leg, which was originally White Zetsu's right leg. Under his Akatsuki cloak, both Zetsus wore blue pants and sandals, and had both legs wrapped in bandages, which hid the area where Black Zetsu's right leg's black colouring merged with his white foot. In the anime, Zetsu's fingernails were painted pink and his toenails, as seen in his début, are blue. He also wore his green Akatsuki ring, which bears the kanji for, on his right little finger.

Unlike White Zetsu, Black Zetsu shows no visible orifices at all, his eye consisting of only a yellow iris. Black Zetsu also had white, screw-like dots which protruded out along the edges of his left half where he was attached to White Zetsu. When the two halves split apart, their plant-like extensions would split and hang from the waists of both. Any clothing they were wearing, including their Akatsuki mantle, would split along with them, causing them to later discard their torn clothing. When either of the halves emerged from the ground while split, their plant-like extensions would surround them in a circular pattern. The two also demonstrated the ability to grow an additional leg from their white body mass to substitute for their missing half when split.

After being bisected by Chōjūrō, Black Zetsu detached from his lower half's white body mass and reshaped himself into a new upper body, which still possesses a single eye but no longer has hair. His eye can be "deactivated" or vanishes at all when he possesses a body with a powerful eye (like Rinnegan or Sharingan) he intends to use.

Abilities
While Black Zetsu was merged with White Zetsu, their signature technique was Mayfly, which allowed them to merge with the ground to quickly travel to a new location, though not as quickly as Obito's space–time travelling. This technique was ideal for Zetsu's function as a spy, as it erased his presence as well, and was an ability that both halves as well as other artificial humans could perform. In addition to functioning as a single entity by communicating through their thoughts, Zetsu's two halves were able to split apart, allowing them to act independently. While separated, the two halves could extend roots underground to communicate with each other over long distances.

Black Zetsu is able to "record" the battles he observes, as well as show these "recordings" to others through unknown means. Black Zetsu is also a skilled sensor type, and was able to sense Naruto Uzumaki and Killer B as soon as they escaped the barrier surrounding the Island Turtle, despite being a vast distance away, though it is unknown if he is able to perform it without White Zetsu's body mass attached to him. As a manifestation of Madara's will, Black Zetsu is able to telepathically communicate with Madara. Black Zetsu has also shown the ability to alter his form and shape. Should he be bisected, he can also regenerate his missing half and likewise attach himself to others, allowing him to control the target's body and use their abilities as his own if they are in a weakened state. Black Zetsu melding with somebody also has the effect of keeping them alive, allowing them to temporarily survive such things as using a sacrificial technique or having a tailed beast extracted from them. However, should the target regain control of themselves, they can prevent Black Zetsu from detaching himself, thus using this trait against him. Like his creator, Black Zetsu has also shown the ability to imbue his will into his targets, which rendered even Madara unable to move or resist.

Dōjutsu
In the attempt to help Madara retrieve his original eyes, Zetsu, after controlling Obito's body, was able to steal possession of the latter's Rinnegan while almost completely removing himself from his body. This, however, would prove temporary when Zetsu was finally able to return it back to Madara, in exchange for the former's left eye. Wielding the Mangekyō Sharingan newly implanted within him, Zetsu is able to utilise Kamui. Bestowed with all its power, Black Zetsu is able to transverse back and forth through the other dimension, all while bringing another person with him, simultaneously.

Nature Transformation
While attached to half of White Zetsu, Black Zetsu has access to Hashirama's cellular material, allowing him to utilise the Wood Release kekkei genkai, albeit on a much weaker scale. Black Zetsu accomplishes this by transforming his white body mass and plant-like extensions into roots during battle.

Sasuke Retrieval Arc
After Sasuke and Naruto's fight at the Valley of the End, Kakashi and Pakkun appear to bring Naruto back home. As the three begin the journey back home to Konoha, Zetsu appears from the ground, having witnessed the whole battle. Later his silhouette appeared with the rest of the Akatsuki members where they discussed Orochimaru taking Sasuke Uchiha, the capturing of the Nine-Tails and the furthering of their plans.

Kazekage Rescue Arc
During the extraction of the One-Tail, Zetsu is told by the Akatsuki Leader to use his real body to use as a lookout, in which he identifies several enemies such as Team Guy, Team Kakashi, as well as Chiyo who was with the latter. Later, he is sent to dispose the corpses of Mukade and Yura, finding Mukade a delicious meal.

After Sasori and Deidara were defeated, Zetsu and Tobi were sent to retrieve their rings, and dispose of their corpses. However, he was unable to eat Sasori due to him being a puppet, but was amazed to finally see what the real Sasori looked like. Tobi found Sasori's ring, wishing to take his place. Black Zetsu thought this was a bad idea, but White Zetsu thought otherwise, noting that Tobi was a good person. They later found Deidara's severed right arm and believe him dead until he arrived and proved them wrong. This caused Black Zetsu to wonder why Deidara hadn't captured Naruto Uzumaki, to which Deidara replied that he had already fulfilled his quota either way.

Hidan and Kakuzu Arc
After Hidan and Kakuzu defeated Yugito Nii, Zetsu appeared to retrieve Yugito, and asked if Hidan was finished with his long winded ritual. When Hidan claimed that they were infidels ignorant of prayers, Zetsu told him that when sad and alone, all one can count on is yourself. Kakuzu, disagreeing stated that money was all one could count on. White Zetsu agreed that money was important, however Black Zetsu stated finding the next one was much more important. Zetsu is later seen sealing the Two-Tails.

Itachi Pursuit Arc
After Deidara's death Zetsu was sent to recover his body, with White Zetsu wondering what happened to Tobi. Black Zetsu mentioned that based on the damaged area, he was most likely caught up in Deidara's explosion. Later, when Pain had encouraged the organisation to mourn Deidara's loss, White Zetsu took it on himself to mourn for Tobi's loss, while Black Zetsu thought such a notion was ridiculous. After Pain's fight with Jiraiya, Zetsu revealed himself to have been watching the whole battle. As Pain announced he was going to capture the Nine-Tails, White Zetsu said it would be an interesting battle and wanted to go. However Black Zetsu had another battle in mind, and they decided to watch Sasuke's battle with Itachi. Both halves spectated and commenting on the battle, with Black Zetsu offering knowledge on various Sharingan abilities. When Itachi died, Zetsu noted that Itachi shouldn't of been that weak, believing him to have already been afflicted prior to the battle. He later appeared near Tobi while he was engaged in combat with the Eight Man Squad, to report to him the result of the fight. They then led Tobi to where Itachi and Sasuke were, with Black Zetsu confirming to Tobi that he had indeed recorded the fight. After a meeting with Taka and Kisame, Tobi met with Zetsu on a bridge where they discussed the fact that Itachi — who had been hampering their plans — was dead and Zetsu lamented on the fact that so many Akatsuki members had died. Tobi said their deaths were worth it because Sasuke was in his hands now.

Invasion of Pain Arc
In the anime, Zetsu was present alongside the other Akatsuki members when they extracted the Six-Tails from Utakata. Zetsu is present when Akatsuki begins sealing the Eight-Tails, and when it is revealed that the jinchūriki fooled Sasuke and replaced himself with a tentacle, White Zetsu flew into a hysterical laughter, which greatly annoyed Black Zetsu. Upon Nagato's death and Naruto returning to the village crowned as a hero, Zetsu revealed himself to have hidden inside a tree, watching the entire fight between them, hardly believing Pain to have been defeated, but decided to relay the information to Tobi. He then returns to Tobi and Kisame, reporting Nagato's death and betrayal, also mentioning that Konan wouldn't be returning either.

Five Kage Summit Arc
Zetsu finds Tobi after the latter had encountered Taka, revealing that Konoha had already been destroyed, and that Danzō had been named the acting Hokage. He then mentioned to Sasuke that Naruto had defeated Pain, and was probably stronger than him. When Taka agreed to go to the Kage Summit, Zetsu split in half. White Zetsu proceeded to lead Sasuke and his team to the Kage Summit while Black Zetsu remained behind and discussed with Tobi the fact that they might lose control over Sasuke and would therefore lose their last chance to have someone sync with the Demonic Statue of the Outer Path. Tobi declared that he was tired of hiding, and explained that they needed to speed up the "Eye of the Moon Plan".

White Zetsu and Black Zetsu meet up at the site of Killer B and Kisame's battle only to reveal that Kisame's decapitated body was actually one of White Zetsu's shape-shifting clones. It is then revealed that Kisame, by having the clone fake his death, was then able to infiltrate Kumogakure while inside Samehada which was being carried back to Kumogakure by Killer B who intended to use it as his own weapon. Black Zetsu then stated that it was their feeding time and that they should merge once again.

Confining the Jinchūriki Arc
In the anime, Zetsu sees off Tobi before he made his journey to Amegakure to retrieve Nagato's Rinnegan. Upon Tobi's acquisition of the Rinnegan, Zetsu informed him that the scroll with the information that Kisame Hoshigaki sent through his messenger shark had arrived, also noting that everything seemed to be going in their favour. Zetsu later accompanies Tobi as he shows Kabuto around the Mountains' Graveyard, but questions if Tobi should really trust him.

Shinobi World War Arc
Supervising Sasuke's recovery, Zetsu told him to be patient when asked if his bandages could be removed, remarking that when he did regain his sight it would be to a different world. As the Fourth Shinobi World War commenced, Black Zetsu separates from White Zetsu separate to carry out his assigned tasks. Before departing, Black Zetsu confirms to Tobi that White Zetsu's spores had been placed on Kabuto's body.

Emerging from the ground near the daimyō's hideout, Black Zetsu infiltrated the structure, despite alerting the enemy to his presence. However, upon discovering the daimyō's absence, Black Zetsu retreated and declared that they shouldn't underestimate his capabilities, as he was a part of the very land itself. Later locating his desired targets, he was instead obstructed by Mei Terumī and her squad, but sensing the Eight and Nine-Tails' chakra while confronting the team, he immediately communicated this to Tobi via White Zetsu. Told that the daimyō were no longer necessary with their quarry now in the open, Black Zetsu was ordered to continue with his guerilla tactics against the Mizukage's team to keep them from regrouping with the rest of their forces. The fight continued throughout the night.

Continuing to battle with Mei and her squad, Black Zetsu observed the arrival of Naruto's shadow clone to their location, who then proceeded to crash into a tree beside him. Growing roots from portions of his body whilst fighting, he used them to trip Naruto and avoid his Rasenshuriken, only to be bisected from behind by the enlarged blade of Chōjūrō's Hiramekarei. Immobilised, Black Zetsu wondered how the sword grew to such a size in an instant and was then sliced in half and pinned to the ground by Chōjūrō's blade as the Mizukage departed. Having been reincarnated, Madara telepathically communicates with Black Zetsu, ordering him to keep watch on Obito until after his "playing" with the Five Kage is done. Subsequently, Black Zetsu seeps into the ground, escaping.

Infinite Tsukuyomi Arc
With Obito weakened after the tailed beasts were extracted from him, Madara enacted his trump card. With this, Black Zetsu suddenly emerged from underground and restrained him. As he began to meld with half of Obito's body, Madara was able to force Obito into using the Outer Path: Samsara of Heavenly Life Technique. Apologising as this all unfolded, Black Zetsu noted that from the start, this was his sole purpose for existing. With Madara's revival a success, Black Zetsu attempts to retrieve Madara's Rinnegan eye from Obito until Minato and Kakashi intervene. Black Zetsu once more melds with Obito's body, using the Uchiha's body to battle his former team and noting that his merger was the only thing keeping Obito alive. While both sides were at a stalemate, the Demonic Statue of the Outer Path emerged from Obito's artificial body, quickly being teleported. Afterwards, Black Zetsu again attempted to take the left Rinnegan. Obito, managing to resist Black Zetsu's control of his hand, told Kakashi to destroy the Rinnegan. Black Zetsu, realising what the summoning of the Demonic Statue meant, informed his enemies that Madara has regained his right Rinnegan.

Standing to face Minato and Kakashi in battle, Zetsu complained about the duo's stubbornness before Gaara arrived along with Sakura and a dying Naruto to their location. Black Zetsu managed to steal Kurama's Yin half when Minato tried to transfer it into his son, thus becoming its jinchūriki. Soon afterwards, Zetsu was joined by Madara who complained about having to come all the way there. As Black Zetsu attempted to return to Madara, bringing with him Yin-Kurama and Madara's missing eye, Obito overpowered him, keeping him merged to his body and he spoke with and subsequently attacked the legend. As Kakashi and now Obito were determined to save Naruto, the two use their respective Kamui to send Naruto to the other dimension and soon afterwards Obito as well. Once there, under watch of a sceptical Sakura, Obito proceeded to transfer Yin-Kurama into Naruto.

Later, after Madara managed to teleport himself using Obito's original Sharingan, which he took from Kakashi, he overpowered Obito and reclaimed his Rinnegan, allowing Black Zetsu to regain control of Obito's body. Madara also implanted Obito's original Sharingan back into his body in order for Black Zetsu to use its power. When Madara began casting the Infinite Tsukuyomi, Black Zetsu wasn't effected, noting that the moonlight could not shine through the Sasuke's Susanoo due to his Rinnegan. After the genjutsu ended, Madara managed to confront Team 7, but was shockedly stabbed by Black Zetsu from the behind, who admonishes a confused and shocked Madara for believing that he was any different than Obito and that he himself couldn't be used. After a distraught Madara screams that Black Zetsu was supposed to be his will, he declares that he is in reality "the will of Kaguya". Following this declaration, Black Zetsu proceeds to spread all over Madara's body as the latter screams in anguish, whilst forcing out the chakra of all the people caught in the Infinite Tsukuyomi from the ground, and having Madara absorb it, turning him into a gargantuan blob. When it was completely covered by Black Zetsu, Madara's body shrunk and changed, bringing forth the revived Kaguya in his place.

Naruto 6: Road to Ninja
Zetsu was responsible for sending several clones disguised as deceased Akatsuki members to attack Konoha at the beginning of the movie. Later, he was seen with Tobi after Naruto and Sakura returned to their world, noting that they were so close to capturing the Nine-Tails.

Creation and Conception
In Naruto Hiden: Sha no Sho Character Official Data Book, Kishimoto revealed that he had originally planned for Akatsuki to be a group of monsters, "with almost no human characteristics", and that Zetsu's design was modelled after an insectivorous plant. He also stated that he had decided to make Zetsu half black and half white to "better show his split personality".

Trivia

 * According to the databook:
 * Zetsu's hobby is observing unique shinobi.
 * Zetsu wishes to fight people who are likely to leave behind a corpse that will make a good meal.
 * Zetsu's favourite food is "chewy" people, while his least favourites are konnyaku and jelly.
 * Zetsu's favourite phrase is, which roughly means "The only one you can count on is yourself".
 * Wherever Tobi is, Zetsu is never far behind.
 * Oddly enough, after escaping from Chōjūrō in his real shapeless form, Black Zetsu is then seen already possessing another White Zetsu-like body mass when attacking Obito. This white mass completely disappears when Black Zetsu merges with Obito's body, but then is immediately restored when Black Zetsu leaves Obito's body. And it finally disappears again when Black Zetsu merges with Obito for the second time. It is unknown if Black Zetsu uses some White Zetsu's spores or can regrow his white body mass himself.
 * The name means "tongue". A fitting name, considering how Madara referred to the two halves of Zetsu  and  based on their personalities.

Quotes

 * (To Tobi about joining Akatsuki) Black Zetsu: "Idiot, it's not that simple." White Zetsu: "It'll be all right, after all, Tobi is a good boy."
 * (To Hidan) White Zetsu: "When you're sad and alone…" Black Zetsu: "…The only one you can count on is yourself."
 * (To White Zetsu) "A weapon's strength or weakness is dependent on the user's ability to use it. An expert with a pebble can still beat a novice with a shuriken."
 * (To Sasuke) "Not yet. Be patient." White Zetsu: "The next time you open your eyes you'll be seeing a whole new world… things are getting really fun!"
 * (To Minato and Kakashi) "I'm Madara's will. I'll eliminate whoever stands in his way. You and Obito took Madara way too lightly, and you underestimated me as well."
 * (To Madara) "That's not true either! My will is… Kaguya."