Tobirama Senju

, the, was the younger brother of the Hashirama Senju (the First Hokage) and the granduncle 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. When the First Hokage, Hashirama, died, Tobirama was appointed as the Second Hokage. He was responsible for establishing Konoha's organisational system by setting up various organisations, such as the Academy, the ANBU, the chūnin exams, and the Konoha Military Police, which he created as a sign of trust towards the Uchiha clan. However, according to Madara, the Military Police was actually established 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. After giving the title of Hokage to Hiruzen, Tobirama went off to fight in the First Great Shinobi World War, where he died a noble death in battle.

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 Bullet Technique with only one hand seal (use of the jutsu normally requiring 44 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.
 * Tobirama is a playable character in the Naruto: Ultimate Ninja series.

Quotes

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