Tobirama Senju is the second Hokage, famous for creating the Edo Tensei jutsu that brought the souls of the dead back to life, now used by Orochimaru and Kabuto.
He was the younger brother of the 1st Hokage and grand uncle of Tsunade. He taught the 3rd Hokage and established Konoha's military, police, and academy. He was the best taijutsu user of all Hokages.
Tobirama Senju was the younger brother of Harishama Senju who was the 1st Hokage. After Harishama's death Tobirame became the 2nd Hokage. Konoha's military, police, and academy. He was a great taijutsu user. Tobirama Senju was more passionate and enthusiastic compared to his calm and prudent older brother, the First Hokage.
He didn't trust the Uchiha, worried they may eventually follow Madara's footsteps, so he appointed them the village's police force as a show of good grace, however he had ulterior motives, getting them to gather in one place in order to better keep an eye on them. Some found out and suspected that Madara may had been right, that they would be subjugated by the Senju.
While on a mission with his team, Hiruzen, Homura, Koharu; aswell as Danzo, Kagami, and Torifu, they were being tracked and were greatly outnumbered by the Cloud village's Kinkaku Force. It was suggested that one of them would have to serve as a decoy for the others to escape and Hiruzen volunteered, however Tobirama told them that he would be the decoy. Danzo insisted against it, saying that he's the Hoakge, however he passed the mantle of Hokage to Hiruzen before he left.
Many years later, Orochimaru discovered how to use Tobirama's Resurrection to the Impure World and brought back both Tobirama and Hashirama, which impressed Tobirama. The reunion however was short-lived when Orochimaru forced them to battle Hiruzen. At the end, Hiruzen used Minato's Reaper Death Seal to kill him and Hashirama, trapping them in the Shinigami.
Nindaime trains Sandaime
Nindaime find out Sarutobi and his protencionals. Nindaime trained Sarutobi and after Nindaime's death Sarutobi became the 3rd Hokage
Powers/Techniques Tobirama was a master water user, even able to use water jutsu without needing a source of water. The full range of his abilities are unknown. Tobirama also possessed the "Raijin Sword," a sword that could generate electricity.