Tobi (Zetsu)

, nicknamed by Obito Uchiha for the swirl pattern of his face, was one of the first victims of the Infinite Tsukuyomi, and eventually was pulled from the Demonic Statue of the Outer Path by Black Zetsu.

Background
He was originally a human victim of Kaguya Ōtsutsuki's Infinite Tsukuyomi, who was tethered to the God Tree until transforming. He was ultimately stored within the Demonic Statue of the Outer Path, where he remained until the statue was summoned by Madara Uchiha, who used it to cultivate Hashirama Senju's DNA to produce a large flowering tree. Black Zetsu then removed him and White Zetsu from inside the statue and modified with Hashirama's DNA, leading Madara to believe they were imperfect clones of Hashirama.

Serving as one of Madara's minions, he met and befriended Obito Uchiha shortly after the latter was brought beneath Mountains' Graveyard and saved by Madara, being designated the task of making sure the young Uchiha was of use to Madara when he woke up. He, along with White Zetsu, enjoyed annoying and teasing Obito about things such as what he murmured in his sleep and human bodily functions. Over time, the duo became friends with the young Uchiha. During this time, Obito coined the nickname Guruguru based on his appearance, a nickname that would eventually stick.

Months into Obito's rehabilitation, White Zetsu returned to the underground base and urgently alerted Obito that he saw Kakashi Hatake and Rin Nohara being cornered by Kirigakure shinobi while he was outside. Resolving to save his friends and return home, Obito tried to break the huge stone blocking the exit in an effort to escape, but destroyed his artificial arm, only cracking the wall in the process. Seeing how desperate Obito was, Tobi noted that his limbs were not strong enough to break through stone yet, and offered himself as a suit of sorts for Obito to wear in order to make it to the surface. Although Obito was skeptical about whether they had permission to help, White Zetsu noted that it would be fine.

Attaching himself to Hashirama's living clone in order to access the power of the Demonic Statue, Tobi was able to break the rock barring the passage way. Opening himself up to form a hood of sorts and encasing Obito, the pair mobilised with Tobi giving directions to the young Uchiha. While en route, he offered to fight in Obito's stead, seeing the young man as weaker than himself. When this offer was refused, Tobi informed Obito of the added benefit of the access he now had to Hashirama's DNA because of his artificial body, stating that due to obtaining the Senju's powers through the infusion of Hashirama's cells, by combining those powers with his own, Obito could awaken an unusual power. Pointing Obito toward the location where giant bodies of water were being displaced, Tobi and Obito arrived to find Kakashi's hand run through Rin's chest, killing her instantly as a horrified Obito looked on.

After witnessing Rin's death, Tobi watched as Obito, now consumed by a strong, overwhelming urge of grief and anger viciously and brutally slaughtered the Kirigakure shinobi at the scene using a combination of Kamui and Wood Release — the latter of which he marveled that the young man could already use, stating that he now understood why Madara had chosen the young Uchiha as his apprentice. After returning to the Mountains' Graveyard and watching Madara pass away, Tobi would remain attached to Obito for some time, accompanying him and Zetsu to Amegakure, where they confronted the Ame Orphans.

Personality
When first meeting Obito, Tobi was playful and enjoyed teasing him about things such as what he murmured in his sleep. Although Obito was initially greatly annoyed by him, the two befriended each other during the former's rehabilitation. Tobi believes that the Eye of the Moon Plan is good for mankind, and sees Madara as a benevolent man. He is also kind-hearted, as shown when he and White Zetsu decided to help Obito without Madara's permission. Because he does not carry out normal bodily functions, he is very curious to know about the mechanics behind them, particularly those involving feces.

By the time of the Fourth Shinobi World War, Tobi had become noticeably more serious, more akin to how Obito became, although he retained his fascination with human bowel movements. He also seemed to be sadistic, reveling in taking lives as a form of relief.

Appearance
Tobi was fully white and could be easily distinguished by the spiral-pattern that stretches all over his body, ending in a circular eye-hole. This pattern did not cover his forearms and legs, but could open up in a similar manner to the flytrap extensions of the original Zetsu to reveal that he is hollow inside. Tobi showed no visible orifices at all, but had a fully defined body. Both while encasing Obito and while fighting in the Fourth Shinobi World War, Tobi wore an indigo cloak.

Abilities
Tobi was a hidden ally Madara Uchiha kept in the shadows after Obito Uchiha used him against the Kirigakure shinobi. Upon his reappearance in the Fourth Shinobi World War, due to encasing Yamato inside him, his abilities had advanced to the point where he could battle thousands of weakened members of the Allied Shinobi Forces, including four Kage, simultaneously.

Body Structure
Tobi was presumed to have the standard abilities White Zetsu possess, such as their signature Mayfly. Tobi and White Zetsu claimed to have vocabularies and brains that surpass those of humans. Like White Zetsu, Tobi could survive without food or water and did not need to carry out normal bodily functions.

Tobi had displayed the ability to open up his top half entirely and use himself as a suit of sorts to encase someone in. By attaching himself to Hashirama's artificial body and using the power of the Demonic Statue of the Outer Path, Tobi was able to greatly augment his strength to the point that he was able to destroy a boulder with a single punch. Due to his extraordinary body structure, Tobi was highly durable and resilient, as he took minimal damage from Suigetsu Hōzuki's point-blank Water Gun Technique and recovered from the effects of a cursed seal in seconds. Likewise, during the few seconds it was paralysed, Tobi was still able to mould its chakra and control its activated techniques.

Nature Transformation
Tobi's genetic material was nearly identical to Hashirama's, and he had access to Wood Release, albeit on a much weaker scale than Hashirama himself. Tobi had knowledge of several Wood Release techniques, and was able to identify Obito's use of the Wood Release: Cutting Technique. During the Fourth Great Shinobi War, seemingly as a result of encasing an incapacitated Yamato, Tobi's abilities increased dramatically. He was able to create a giant wooden statue, through which he could simultaneously perform techniques of all five elemental nature transformations, as well as utilise the wooden statue's thousand arms with devastating effects.

Birth of the Ten-Tails' Jinchūriki
At some point after Madara's revival, Tobi appeared on the battlefield to buy the Ten-Tails time to revive so Madara could become its jinchūriki and started fighting the Allied Forces with a gigantic wooden statue. Informing his opponents that he would never let them go so easily, he asked whether or not anyone would take his question seriously, which was how he felt to have a bowel movement, but shrugged it off, assuming that it resembled the satisfaction of taking another life. Observing the situation on the battlefield, Tobi was greeted by a White Zetsu clone, who told him that Naruto was of the Uzumaki clan, and thus could temporarily resist death from having the Nine-Tails extracted from him, but the two simultaneously affirmed that Naruto was doomed to die.

After impaling Karin with the Wood Release: Cutting Technique in an attempt to stop her from saving Sasuke Uchiha's life, the left side of his head was shattered and it was revealed that someone was inhabiting his body. Though his movements were temporarily stopped by Orochimaru's cursed seal, Tobi mused that their efforts were in vain nonetheless. When Madara initiated the Infinite Tsukuyomi, Tobi abruptly stopped fighting the Allied Forces and noted that his job was done before unceremoniously ejecting Yamato from his body, noting that he no longer had a need for him either.

Kaguya Ōtsutsuki Strikes
After the Infinite Tsukuyomi was dispelled by Naruto and Sasuke, Tobi was seen dying, grasping desperately at Yamato while breaking apart into pieces.

Video Games
Obito wearing Tobi's body as a suit appears as a playable character in Naruto Shippūden: Ultimate Ninja Storm 4. He is also fought twice in story mode as a non-playable opponent. When fought, he uses the same moveset as Tobi, except with a generic awakening.

Trivia

 * Tobi's face resembles the mask Obito wore prior to the Fourth Shinobi World War, and his personality also resembles Obito's when he was acting as Deidara's partner. In fact, his name in the fourth databook is "Tobi", which Obito used while wearing the mask. In English he even shares the same voice as Obito's "Tobi" persona.
 * His nickname comes from Obito calling him, which is an onomatopoeia for turning round and round or going around in circles. It can also mean wrapped around, referring to Tobi's function as an armour for Obito. This name was later confirmed in a special page added to Issue #14 of Weekly Shōnen Jump.
 * Tobi is unique in appearance and personality resulting from mutation after being trapped inside Kaguya's Infinite Tsukuyomi; all others share the same appearance.