Tobirama Senju (千手扉間, Senju Tobirama) was a member of the renowned Senju clan, who, together with his elder brother and the Uchiha clan, founded the first shinobi village: Konohagakure. Throughout his lifetime, Tobirama would work tirelessly to achieve political stability and implement the institutions that made the village system work, thus ensuring Konoha's continuity and prosperity. After his brother's death, he would succeed the title of Second Hokage (二代目火影, Nidaime Hokage, Literally meaning: Second Fire Shadow).
Tobirama was born during the Warring States Period, and was the second of Butsuma Senju's four sons. He and his brothers grew up on the battlefield waging constant war with their rivalling clans especially the Uchiha. After the deaths of their brothers: Kawarama and later Itama, Tobirama and his older brother, Hashirama, decided a new shinobi system would need to be implemented to end the cycle of child deaths — a system that would require an alliance between the warring clans. At some point in time, it became apparent that Hashirama got into the habit of disappearing into the forest for extended periods, and as such, Tobirama accepted his father's assignment to follow Hashirama and find out what he was doing.
From tracking Hashirama, Tobirama discovered that he was meeting with a boy named Madara: a young Uchiha. After Tobirama reported this to their father, Butsuma pressured Hashirama to lead Madara into an ambush to be carried out by himself and Tobirama. Upon springing the trap, however, they were met by Madara's family — who had similar plans and while their fathers clashed — Tobirama fought Izuna Uchiha: Madara's younger brother. Hashirama and Madara were able to negotiate a temporary ceasefire, allowing all of them to walk away without bloodshed. In the years following their families would continue to clash, Hashirama against Madara and Tobirama against Izuna. On one occasion Tobirama eventually mortally wounded Izuna.
Hashirama, by then the leader of the Senju, tried to use Izuna's fate to broker peace between their clans, but Madara — at Izuna's behest — refused. His refusal increasingly became the minority view, with individual Uchiha siding with the Senju in growing numbers. After Izuna succumbed to his injuries, Madara, wracked with grief, made one final stand against the Senju and was summarily defeated. Tobirama attempted to kill Madara to finally end the fighting, but Hashirama stopped him, knowing that would only renew hostilities between the Senju and Uchiha. Madara offered to surrender if Hashirama would kill himself or Tobirama. Hashirama agreed to take his own life, and as he made preparations he instructed Tobirama, despite his protests, not to seek retribution. Madara ultimately withdrew his request and agreed to peace.
The Senju, the Uchiha, and all their affiliated clans came together to found Konoha, a village of peace where children would never need to die in battle. Although Hashirama was optimistic about the village's future, Tobirama remained realistic about how that future would be achieved knowing that it was not enough to simply bring all these clans together. He believed the Uchiha — Madara in particular — threatened that future. When Hashirama wanted to give Madara the position of Hokage, Tobirama forced him to open the selection to a democratic process rather than appointing a leader, leading to Hashirama's election instead. Tobirama would continue to act as the voice of reason throughout Hashirama's tenure; during the first Kage Summit, Hashirama wanted to give Konoha's tailed beasts to the other newly-formed villages for free, but Tobirama insisted that the villages pay for the tailed beasts they received.
Under Hashirama's leadership, the new system of ninja villages achieved peace for a time. Eventually, Tobirama started training his own three-man team consisting of Hiruzen Sarutobi, Homura Mitokado, and Koharu Utatane. Techniques he had created, such as the Shadow Clone Technique and Summoning: Impure World Reincarnation, he outlawed, their use no longer being needed. But peace would ultimately be temporary as Madara challenged Hashirama's authority and the two fought at what would become the Valley of the End. When Madara was killed in the battle, Tobirama took his body in order to study the Sharingan, and then buried it in an unmarked grave. Conflicts would start emerging elsewhere in the world, and it was during one of these that Hashirama would die. Before his death, he passed the title of Hokage to Tobirama and left him instructions to not mistreat the Uchiha.
Tobirama's role as Hokage included helping Konoha's shinobi transition from valuing their clan above all else to valuing the village and everyone in it. To this end he created such institutions as the Academy, the Anbu, and the Chūnin Exams. While largely successful, enough that other villages adopted the same organisations, the Uchiha resisted the loss of their autonomy. Already wary of the Uchiha because of his history with Madara, Tobirama created the Konoha Military Police Force for the Uchiha to run, publicly as a sign of trust but primarily so that the Uchiha could focus their energies into something beneficial. Others, however, would come to see this as a way to marginalise the clan.
Like Hashirama before him, Tobirama tried to foster good relations with the other villages. He planned an alliance between Konoha and Kumogakure, but during a formal ceremony he and the Second Raikage were attacked by the Gold and Silver Brothers and left near death.During the First Shinobi World War, Team Tobirama, as well as Danzō Shimura, Torifu Akimichi, and Kagami Uchiha found themselves surrounded by Kumo's Kinkaku Force. With no way for all of them to escape, Tobirama volunteered to act as a decoy in place of Hiruzen. As he departed, he passed the title of Hokage to Hiruzen, before being killed by Kinkaku.