Tobi (Zetsu)

is an artifically created clone of White Zetsu, being a subordinate of Madara Uchiha and was assigned to aid Obito Uchiha alongside White Zetsu during the young Uchiha's rehabilitation.

Background
He was one of many artificial humans created using the Demonic Statue of the Outer Path and Hashirama's living clone, in particular being a clone of the original artificial human, White Zetsu. Serving as one of Madara Uchiha's loyal minions and spies, he met and befriended Obito shortly after the latter was 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 bodily functions. Over time, the duo became friends with the young Uchiha.

Months into Obito's rehabilitation, White Zetsu returned to the underground base and urgently alerted Obito that he saw Kakashi and Rin being cornered by Kirigakure shinobi while he was outside. Resolved to save his friends, 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, the spiral-patterned Zetsu 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 sceptical about whether they had permission to help, White Zetsu noted that it would be fine.

Attaching itself to the living clone in order to access the power of the Demonic Statue, Spiral Zetsu is able to break the rock barring the passage way. Opening up itself to form a hood of sorts, the pair mobilise with Spiral Zetsu giving directions to the young Uchiha. While en route, the clone offers to fight in Obito's stead seeing the young man as weaker than himself. When this offer is refused, Spiral Zetsu informs Obito of the added benefit of the access he now had to Hashirama Senju's DNA because of his artificial limbs. Pointing Obito towards the location where giant bodies of water is being displaced, the clone and Obito arrive to find Kakashi's hand run through Rin's chest.

After Obito and the clone witness Rin's death, Spiral Zetsu witnesses as Obito slaughters the opposition using a combination of Kamui and Wood Release — the latter of which the clone marvelled that the young man could already use, stating that he now understood why Madara had chosen the young Uchiha. After this incident, Spiral Zetsu would remain attached to Obito, accompanying him to Amegakure, when he confronted Nagato.

Personality
When first meeting Obito, Spiral Zetsu was playful and enjoyed teasing him about things such as what he murmured in his sleep. Although Obito was initially greatly annoyed by the pair, the two befriended each other during the former's rehabilitation. He 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 decide 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.

During the Fourth Shinobi World War, Spiral Zetsu's personality 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
Spiral Zetsu is fully white and can be easily distinguished by the spiral-pattern that stretches all over ending in a circular eye-hole. This pattern does not cover his forearms and legs, but can open up in a similar manner to the fly-trap extensions of the original Zetsu to reveal that the clone is hollow inside. This Zetsu shows no visible orifices at all, but has a fully defined body.

During the Fourth Shinobi World War, he wears a black cloak while fighting the Allied Forces.

Body Structure
As a clone, Spiral Zetsu is presumed to have the standard abilities all clones normally possess, one primary being their signature Mayfly. Spiral Zetsu and White Zetsu also claim to have a vocabulary and brain that surpasses that of a human's. Being an artificial human created from Hashirama's cells, he can survive without food or water and needs to carry out no normal bodily functions.

Spiral Zetsu has also displayed the ability to open up his top half entirely, and use himself as a suit of sorts to encase someone in. By attaching itself to Hashirama's living clone and using the power of the Demonic Statue of the Outer Path, Spiral Zetsu was also able to greatly augment his strength to the point that he was able to destroy a boulder with just a single punch.

Due to his extraordinary body structure, Spiral Zetsu is highly durable and resilient, as he took minimal damage from a point-blank Water Gun Technique from Suigetsu and recovering from the effects of a cursed seal in moments.

Nature Transformation
As an artificial human, created through the Demonic Statue of the Outer Path using Hashirama Senju's DNA, Spiral Zetsu has access to Wood Release, albeit on a much weaker scale than Hashirama himself. Spiral Zetsu also seems to have knowledge of several Wood Release techniques, as he was able to discern that Obito was using the Wood Release: Cutting Technique when the Uchiha first used it.

By the time of the Fourth Shinobi World War, Spiral Zetsu's abilities increased dramatically, as he was able to use Sage Art: Wood Release: True Several Thousand Hands, one of Hashirama's most powerful ninjutsu — albeit without the senjutsu enhancement, resulting in a smaller scaled version — and with it he is able to wield all five basic nature transformations simultaneously.

Return of Madara Arc
After Madara's revival, Spiral Zetsu appeared on the battlefield and started fighting the Allied Forces with Sage Art: Wood Release: True Several Thousand Hands. 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 it felt to have a bowel movement, but shrugged it off, guessing that it resembled the satisfaction of taking another life. Observing the situation on the battlefield, Spiral Zetsu was greeted by a White Zetsu clone who told him that Naruto was of the Uzumaki clan, and thus could 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 attempting to stop her from saving Sasuke's life, the left side of his head was shattered momentarily, and it was revealed that someone was inhabiting his body. Though his movements are temporarily stopped by Orochimaru's cursed seal, Spiral Zetsu mused that their efforts were in vain nonetheless.

Trivia

 * Spiral Zetsu'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.
 * His name 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 Spiral Zetsu's function as an armour for Obito.