Tobirama Senju

, the, was the younger brother of the Hashirama Senju (the First Hokage) and the great-uncle of Tsunade (the Fifth Hokage) and Nawaki.

Background
Tobirama was part of the Senju clan, along with his leader and brother, Hashirama. When, decades before the start of the series, Hashirama struck a peace treaty with Madara Uchiha, Tobirama helped them to found Konoha. After Madara defected from the village and Tobirama was appointed as the Second Hokage, he created the Konoha Military Police as a sign of trust with the Uchiha clan. According to Madara, this was actually done to distance the Uchiha from the government of the village, and place the clan under a tight surveillance under the ANBU.

Tobirama trained a three-man team of his own called Team Tobirama, which consisted of Hiruzen Sarutobi, Homura Mitokado, and Koharu Utatane. He eventually selected Hiruzen, his prized student, for the position of Third Hokage, Homura and Koharu becoming Hiruzen's advisers. Tobirama would later die on the battlefield.

Personality
From what has been seen of Tobirama, he had pride in his abilities involving water jutsu. He also had a sense of humor, even under stressful situations. Like his brother, Tobirama felt a great deal of loyalty to the village, and placed its well-being above his own.

Invasion of Konoha arc
Both he and Hashirama were revived from the dead by Orochimaru, using Impure World Resurrection, to fight Hiruzen during the invasion of Konoha. While fully aware of what was going on, and saddened that he would have to fight his former student, Orochimaru employed a special seal to rob Tobirama of his free will. His soul was eventually sealed by Hiruzen with the Dead Demon Consuming Seal, along with his brother and Orochimaru's arms. Before his soul was completely removed, he and his brother apologized to their former student for the trouble they had caused.

Abilities
Tobirama was primarily known for his mastery of Water Release jutsu, being able to make use of powerful water jutsu in areas where there were no bodies of water. He could manipulate it to form projectiles or tentacles, and could even perform jutsu like the Water Release: Water Dragon Blast Technique with only one hand seal (use of the jutsu normally requiring 42 hand seals).

In an anime filler arc, it was said that he wielded the Sword of the Thunder God, a blade with electrical abilities, and was said to have mastered its use despite the lethality. He is also shown to have great physical prowess and taijutsu skills.

Trivia

 * Tobirama is the brother of the First Hokage, trained the Third Hokage, and is the granduncle of the Fifth Hokage.
 * Tobirama is known as the greatest water manipulator that ever existed.
 * In the omake at the end of Shippūden episode 2, Naruto stated that Tobirama was the man with the best combat ability.

Quotes

 * "Do you hear? Guide the people, and believe in them, for it's from among them that the one will come who will carry on when your time is done ... starting tomorrow, you are Hokage!"