Tobirama Senju

, the is the younger brother of 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. Eighty years prior to the current era, the world was in a time of war and the ninja clans were nothing more than assassins for hire for the various feudal lords. Because of his brother, the Senju clan was constantly being hired for wars and in turn the enemy would then hire the Uchiha clan. However, Hashirama soon found it meaningless to continue fighting and offered the Uchiha clan a truce - something that their leader, Madara Uchiha was reluctant to agree, but was pressured into accepting by his own clansmen.

Eventually, the allied Senju clan and Uchiha clan would make a pact with the feudal lord of the Land of Fire and the Tobirama would together with his brother and Madara foster the village Konohagakure, and helped create the "one village per country" rule that would eventually end most of the wars between the feudal lords, but their armies were still maintained at current level by the five great shinobi countries after the first ninja war. However there were still internal struggles and after the fight between Madara and Hashirama, the villagers soon began suspecting the Uchiha clan of treason and plotting against the village, but Hashirama, taking the Uchiha clan's word, chose to do nothing.

During this time, Tobirama trained a three person team of his own called Team Tobirama, which consisted Hiruzen Sarutobi, the future Third Hokage, and Homura Mitokado and Koharu Utatane, the two future elder advisers of the village.

However, the war still waged on and unsure of the title of Hokage, Hashirama would appoint his brother as the Second Hokage, and later Tobirama would also appoint his prized student, Hiruzen to be the Third Hokage.

After becoming the Hokage, Tobirama would give the Uchiha clan a special position as a sign of trust. He gave them the leadership of the Konoha Military Police. However (according to Madara), this was just a cover up, and its true purpose was just to distance the Uchiha from the government of the village, and place the clan under a tight surveillance under the ANBU.

Like his brother, Tobirama had a true loyalty to his village and believed strongly in peace. He too would eventually die in the wars, and pass on the title of Hokage to his student Hiruzen.

Invasion of Konoha arc
Both he and Hashirama were later revived from the dead by Orochimaru using Summoning: Impure World Resurrection to fight Hiruzen Sarutobi during the invasion. His soul is eventually sealed into the stomach of the Death God, along with his brother and Orochimaru's arms.

Anime filler arcs
During the anime's Tea Country filler arc, it was revealed that Tobirama possessed a valuable retractable energy sword called Sword of the Thunder God. Despite its appearance as an arc of lightning, the blade can be cracked and broken like a regular sword, as shown at the end of the arc.

Water Release
Primarily known for this, he was hailed for being the greatest master of Water Release jutsu, being able to make use of powerful Water jutsu in areas where there were no bodies of water.

Beyond his formidable ability to create (or gather) water his prodigious skill with water jutsu also extended to cutting out a significant portion of the hand seals used to mold a jutsu. For example, the Water Release: Water Dragon Blast Technique usually requires the largest amount of hand seals ever seen in the Naruto Universe, 42 hand seals, however he is shown to only require one hand seal.

Also, during his fight against Hiruzen, in the anime only, he displays great abilities in manipulating water, such as using it for projectiles, or tentacles to drag the opponent down in the water. He also displayed tremendous taijutsu and genjutsu prowess, in addition to remarkable tandem combat sync with his brother.

Close Range Fighting
In an anime filler arc, it was said that he wielded the Sword of the Thunder God, a blade with electrical abilities and is said to have mastered its use to lethality. He is also shown to have great physical prowess and taijutsu skills. In the anime, he is shown to be able to use the Bringer-of-Darkness Technique to enhance his ability to land hits.

Trivia

 * Tobirama is the brother to the First Hokage, trained the Third Hokage, and is the granduncle to the Fifth Hokage.
 * Despite being the First Hokage's brother, Tobirama's skin, hair and eye colour are all very different from the First's.
 * It can be noted that the colouring of the First Hokage and Second Hokage greatly resembles that of Iruka Umino and Hatake Kakashi, respectively.

Quotes

 * ''Do you hear? Guide the people and believe in them for its from among them that the one will come who will carry on when your time is done...starting tomorrow, you are Hokage!
 * (To Sarutobi)''Its been long time ,eh monkey...