Zetsu

is a member of Akatsuki who functions as the organization's spy and potential army.

Personality
According with his two differently colored halves, Zetsu seems to have a split personality, as in the Japanese version of the manga, the black half of his face only uses katakana for okurigana and furigana while the white side uses kanji and kana regularly. The two halves also converse with each other, and occasionally differ in opinion (the black half is more serious and intelligent while the white half is carefree, easygoing, and seems to enjoy toying with others). They also seem to communicate through their thoughts.

Zetsu is seemingly very trustworthy, being entrusted with knowledge of Pain and Tobi's true identities. He has apparently been working with the latter for some time, Tobi first appearing as his "subordinate" and Zetsu later commenting that Tobi's plans had been in the works for a long time. The character showed some lust for money when he quoted Kakuzu on his principle that money is most important. However, whether or not this applies for both personalities is as of yet a mystery to be dealt with. Zetsu's white side has also shown to be very confident in himself as he was willing to fight Naruto despite knowing Pain had lost in battle against him.

Zetsu's main role within the Akatsuki is to function as a spy, and often performs duties that are similar to a hunter-nin. He has been shown able to move his body and take part in the tailed beasts 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 to Akatsuki, or possibly even a member, dies, Zetsu is sent to devour their bodies so as to not have their secrets revealed, which adds further his venus fly trap theme. 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. Despite this, Zetsu serves as a sort of superior to other members, as they often reported directly to him instead of to the actual leader, Pain.

Appearance
Zetsu is easily distinguished by two large venus flytrap-like extensions that envelop his head and upper body, giving him a plant-like appearance. When his extensions are open and his head is visible, it is revealed that Zetsu has short green hair, yellow eyes, and that his body has two different colored halves, his left side is completely white and the right side black. The black color doesn't extend all the way down Zetsu's body, as his feet are both white and in the anime his hands are also white. When he splits into two the plant like extensions go down the waist and now have the appearance of spikes, each halve has half of the Akatsuki robe and the halve they are missing is replaced with new body mass.

Unlike the white side, which shows a normal mouth, nose, and eye, the black side shows no visible orifices at all and only shows the iris of the eye. The black half also has white dots along the edges of his body where the two halves meet; these are not flat markings, but rather protrude from his body, like little white bumps. Zetsu also has unusually rounded teeth. He wears red nail polish on his fingers (his toenails, seen at his debut, are bluer) and wears his ring on the right little finger. In the manga, Zetsu does not have fingernails however.

The White Zetsu's of Madara's army, however, are slightly different. Unlike the original, they have a complete face and a proper right arm and leg. They also seem to have small spikes protruding from their shoulders and on their back, but lack the venus flytrap-like extensions.

Abilities
Zetsu has yet to be seen in battle but Madara refers to Zetsu as not being a "front line" fighter. The technique he has been shown using the most is his Mayfly technique, with which he merges with the ground to instantly travel to a new location, though he isn't nearly as fast as Madara's space-time traveling. This technique makes it ideal for Zetsu's function as a spy, as it erases his presence as well. It has also been noted that Zetsu has the ability to "record" the things he sees, as noted when he tells Madara Uchiha that he had recorded the whole battle between Sasuke and Itachi, and between Kisame and Killer Bee. It is unknown how he is able to show these "recordings".

Zetsu has also shown the ability to split in two, so that his two personalities can act independently. He is also able to use a time-delayed spore jutsu to grow into a mushy mass around several individuals at once, thereby sucking their chakra out, and can even use it to replenish another persons' chakra. Zetsu's white half has also shown the ability to create multiple copies of himself. Zetsu can create a special clone which can simulate the appearance anyone Zetsu has ever touched down to their chakra, but it is much weaker than the original person, and therefore mostly only useful as a diversion and decoy.

The amount of white Zetsu clones that can be created given enough chakra is extraordinary, numbering 100,000, which make up the majority of Madara's Akatsuki army.

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.

Part II
Zetsu appears frequently throughout the series. In addition to serving his various Akatsuki duties, he watches battles of interest and then reports the outcome to the other members, and eats the bodies of dead associates.

Kazekage Rescue Arc
During the extraction of the One-Tailed Shukaku, Zetsu is seen also spying on Team Guy and Team Kakashi and alerting Akatsuki. Later, he is sent to dispose the corpses of Mukade and Yura. Zetsu is present with Tobi when retrieving Sasori's ring and when locating Deidara.

Hidan and Kakuzu Arc
After Hidan and Kakuzu defeated Yugito Nii, Zetsu appeared to get Yugito to start the extraction. When Hidan claimed that Akatsuki was just after money like Kakuzu, Zetsu told him that when he's sad and alone, all you can count on is yourself.

Itachi Pursuit Arc
During the fight between Sasuke and Itachi, he also acted as a commentator, giving the viewers some insight into the techniques both of the Uchiha were performing. He later appeared to inform Madara of the result of the fight and then led him there, where Madara then asked if he had recorded everything, to which Zetsu confirmed.

Five Kage Summit Arc
After Itachi's defeat and Sasuke's recruitment, Zetsu took a more active role in Madara's ongoing plans as now there are only three Akatsuki members left, marveling at the effort that went into getting Sasuke to work with Akatsuki. He was later revealed to have watched the entire fight between Pain and Naruto Uzumaki, and appeared next to Tobi as he argued with Sasuke about what his next objective was. There he revealed that Konoha had already been destroyed. When asked by Tobi, he revealed that Danzō had been named the acting Sixth Hokage. He then proceeded to explain the outcome of the battle between Pain and Naruto. When Taka agreed to go to the Kage Summit, Zetsu revealed his ability to split in half, and the white half proceeded to lead Sasuke and his team to the Kage Summit while the black half remained behind and discussed with Madara 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. Madara declared that he was tired of hiding, and explained that they need to speed up the "Eye of the Moon Plan".

The white half stayed with Taka, currently in the Land of Iron, observing the meeting of the Five Kage and trying to figure out a way to successfully assassinate Danzō. After identifying Danzō, the white half managed to leave Taka and slip into the conference room, telling the five Kage that Sasuke was somewhere around. At that time the black half was with Madara, both hidden in the Land of Iron and received the instruction to "begin".

After revealing himself, the Fourth Raikage grabbed the white Zetsu's neck, asking him the whereabouts of Sasuke, and threatened to use force. Zetsu mockingly replied that he would give a hint. The Raikage, angered, tightened his grip on Zetsu's neck. White Zetsu collapsed on the floor, and everyone there presumed that he died. After Sasuke had been struck by the Fifth Mizukage's Boil Release: Skilled Mist Technique, Zetsu used some kind of Spore Technique, which was secretly implanted in everyone in the meeting hall before the Raikage's attack. The spores leeched some of the chakra of the Mizukage while binding the samurai guards, Mifune, Ōnoki and everyone else. His black half comments on the five Kage being fools, as they failed to detect his spore jutsu. One of the spores then jumped onto Sasuke, but instead gave him the absorbed chakra, allowing him to use an arm of Susanoo to escape from the Mizukage. Everybody is able to remove the spore technique thanks to Kankurō's puppet strings, with the exception of the Five Kage and Akatsuchi (they removed it themselves). Mifune then stabs one of Zetsu's clones through the head. The spores had also been implanted within Kurotsuchi, Ao, Danzō, Fū, and Torune, all of whom had left the meeting hall for various reasons, but they had managed to get the parasitic technique off of themselves.

Zetsu's white half reveals after Sasuke and Naruto clash that Madara told him to keep an eye on Sasuke. Upon calling Madara back, white Zetsu was prepared to fight and capture Naruto while he demonstrated an ability to create several copies of his white half. Before he could engage in combat however Madara tells him not to as he wasn't a 'front line' fighter, and instead gives him the task of checking up on Kisame and to rejoin with his black half.

White Zetsu and his Black half met up at the site of Killer Bee and Kisame's battle only to reveal that Kisame's decapitated body was actually one of their shape-shifting clones. The real Kisame, by having the clone fake his death, was then able to infiltrate Kumogakure while inside his sword, Samehada. The sword itself is being carried on the back of Killer Bee who plans to use it as his new weapon. Black Zetsu then says that it's their feeding time and they should rejoin.

Confining the Jinchūriki Arc
Upon Madara's return to the base, Zetsu, now with his halves rejoined, informs him that the scroll with information from Kisame Hoshigaki sent through his messenger shark had arrived. He also noted that everything seemed to be going in their favor. Kabuto mentioned he could make Zetsu stronger and that he was the key to fight the shinobi forces. Madara promised to give him "one Zetsu" if Kabuto captures the Nine-Tails. Later, Madara revealed to Kabuto a hundred thousand clones of white Zetsu, which will be used to match the numbers of the Allied Shinobi Forces.

The original Zetsu was sent to keep an eye on Sasuke while he's recovering, to prevent Kabuto from getting close. The Zetsu army (presumably strengthened by Kabuto) marches off to war with Madara and Kabuto leading.

Creation
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 modeled 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
Kishi has stated that he plans to do something big with Zetsu, implying he's the final villain.
 * According to Zetsu's card in the Naruto Shippūden card game, he is from Konoha.
 * In the manga, Karin and Zetsu first meet right before the meeting of the five Kages. In the anime, they meet after the fight between Itachi and Sasuke. In addition, she seems much less disgusted by his appearance in the anime.
 * Kishimoto first intended to make Akatsuki's members monsters with almost no human traits. Zetsu is a prime example of this.
 * According to the Third 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 favorite food is chewy people, while his least favorites are konnyaku and jelly.
 * Zetsu's favorite phrase is, which roughly means "The only one you can count on is yourself".
 * Wherever Madara is, Zetsu is never far behind.
 * Zetsu still refers to Madara Uchiha as Tobi.

Quotes

 * (To Tobi about joining Akatsuki) Black side: "Idiot, it's not that simple." White side: "It'll be all right. Tobi is a good boy."
 * (To Hidan) White side: "When you're sad and alone ..." Black side: "... all you can count on is yourself."
 * (When Killer Bee's body turned into a tentacle during extraction) White side: "Ahahaha a tentacle!" Black side: "It's not funny!"
 * (After Naruto called him an insulting name) White side: " 'Aloe vera'?!" Black side: "Just ignore him..."
 * Black side: "An expert with a pebble can still beat a novice with a shuriken".
 * Black side: "The Five Kage are a bunch of fools!"