Tobirama Senju

was the of Konohagakure. He hails from the Senju clan, who, along with the Uchiha clan, founded the first shinobi village: Konoha. During his reign, Tobirama was accredited as the Hokage that developed the village's organisational system as well as some of its infrastructure.

Background
Tobirama was a member of the Senju clan along with his brother Hashirama — who was the leader of the clan. Decades before the start of the series, Hashirama struck a peace treaty with the Uchiha and its then-leader Madara Uchiha and together the two clans created Konohagakure.

When Hashirama, who was appointed the First Hokage, died, Tobirama was appointed as the Second Hokage. During his reign he was primarily responsible for establishing Konoha's organisational system. He established various organisations such as the Academy, the ANBU, the Chūnin Exams and the Konoha Military Police Force, the latter of which he appeared to created as a sign of trust towards the Uchiha who made up the majority of that organisation. The Uchiha would come to believe that this was just an elaborate way to ostracise them from the village, and its government.

At some point during his era, he and the Second Raikage met to form a formal alliance between Kumogakure and Konohagakure; however, Kinkaku and Ginkaku, Kumo's Gold and Silver Brothers, attempted a coup d’etat against the Second Raikage and left Tobirama near death during the fiasco.

He also trained a three-man team of his own, which consisted of Hiruzen Sarutobi, Homura Mitokado, and Koharu Utatane. On one mission during the First Shinobi World War, on which Team Tobirama performed with Danzō Shimura, Kagami Uchiha and Torifu Akimichi, they found themselves surrounded by twenty elite Kumo ninja known as the Kinkaku Force. Tobirama then realised that the only way any of them could escape alive was for one of them to be a decoy and sacrifice themselves; therefore having faith that he had trained his students well, he chose to sacrifice himself after he selected his prized student Hiruzen for the position of Third Hokage. Homura and Koharu would later become Hiruzen's advisers. After giving the title of Hokage to Hiruzen, Tobirama went off to fight the enemies where he died a noble death.

Personality
Tobirama took great pride in his abilities. Like his brother, Tobirama felt a great deal of loyalty to the village, and placed its well-being above all else. Tobirama was also described as being strong-spirited, and passionate.

More straight-laced than his exuberant brother, Tobirama was a realist who took things and people for what and who they were. This was displayed during the First Shinobi World War when he and his small battalion were surrounded by the Kinkaku Squad, Tobirama realised the only way out for his subordinates, and acted accordingly. This was also displayed in his attitude towards the Uchiha whom he believed were almost all intrinsically cursed, based on his knowledge of them, as well as his own personal interactions with them. Between him and his brother, Tobirama had the more assertive personality, easily being able to talk down his older brother who would sulk and obey his commands. Tobirama also cares greatly for the village and, while holding no real love nor loyalty towards the Uchiha, Tobirama valued peace and balance and tried in his own way to help the Uchiha from falling prey to their own unknown curse by placing them in charge of the Konoha Military Police Force, so that history would not repeat itself and create another person like Madara Uchiha.

Appearance
Tobirama was a tall, fair-skinned man with white, shaggy hair, red eyes and three red markings on his face — two under his eyes and one on his chin. In most cases, his attire took the form of the standard shinobi dress of his era, consisting of blue traditional armour — similar to that of samurai — albeit featuring a distinctive white fur collar, worn over a simple black suit. This armour was constructed from numerous metal plates, formed into multiple protective guards along his body, in particular: chest, waist, shoulders and upper arms. This clothing was accompanied by sandals and a happuri engraved with the Konoha emblem, in the place of the more traditional forehead protector.

Outside of this outfit, Tobirama wore a simple, short-sleeved, blue shirt kimono with mesh armour underneath and held closed by a pale yellow sash, as well as blue pants and a bracelet of sorts on his left hand.

Abilities
As the Second Hokage, Tobirama was undoubtedly an immensely powerful shinobi and was hailed as one of the most powerful shinobi of his era. During his lifetime, Tobirama created the Summoning: Impure World Reincarnation technique; however, some time after its creation he labelled it as a kinjutsu and never mastered it himself, though he did use it enough to be recognised by others for it. By simply touching the ground with his index finger, he could detect the presence and number of enemy shinobi, and according to Minato Namikaze, Tobirama was highly skilled in Space–Time Ninjutsu. Tobirama was also shown to have great physical prowess and a considerable amount of skill in the area of taijutsu, as well as good teamwork with his elder brother, Hashirama Senju. In the anime, it was shown that he was also a powerful genjutsu user, able to shroud the area in darkness that even the Third Hokage couldn't dispel. 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 blade's lethal nature.

Nature Transformation
Tobirama was primarily known for his mastery of Water Release. He could perform powerful water-style techniques in areas that lacked bodies of water by creating his own water out of thin air or producing it from his mouth, and perform some of the most complex water-style techniques, such as the Water Release: Water Dragon Bullet Technique, with a single hand seal. This amongst other reasons is why he is revered as the greatest known Water Release manipulator in the series.

In the anime, it is also shown that he can use the Water Release: Water Colliding Wave to attack and cover a large area with water. In areas with water, he can move underwater and stay for a considerable amount of time. Underwater, he can use jets of water to bring his target to him and after restrain them for trying to drown them or launch powerful missiles of water which can even pierce rocks.

Invasion of Konoha Arc
Both he and Hashirama were reincarnated by Orochimaru, using Impure World Reincarnation, 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 into the back of their heads to rob Tobirama and his brother of their free will. Hiruzen quickly resolved to kill his masters and used a very powerful fire technique that was easily countered by one of Tobirama's walls of water that was then turned into an attack that was stopped by Hiruzen's own earth wall.

During the battle, he demonstrated great teamwork and combination attacks with his brother, forcing Hiruzen to summon Enma for assistance. Hiruzen was however in his old age unable to defeat the two Hokage, as any damage that was done was simply regenerated and was further inhibited by his desire to not hurt either. His soul, along with his brother's, was eventually sealed by Hiruzen when he combined the Dead Demon Consuming Seal and the Shadow Clone Technique to strike both of them at the same time. Before his soul was completely removed, he and his brother apologised to their former student for the trouble they had caused.

Shinobi World War Arc
In Sasuke Uchiha's quest to learn the truth, Tobirama's soul was later freed from inside the Shinigami, and subsequently reincarnated by Orochimaru along with his brother, and his two successors: Hiruzen and Minato using Zetsu's spore clones as sacrifices.

Cursing Orochimaru initially, Tobirama and his brother listened on as Hiruzen and Minato explained what had happened. With his arms still crossed, Tobirama looked down the line with his brother at the Yellow Flash questioning who he was, before promptly being shown the haori emblazoned with the title of Fourth Hokage. Not one to side-swept, Tobirama questioned the ease of use Orochimaru displayed with the technique he had invented only to be told the technique was not a hard one to learn but one which should have never been created. Orochimaru's response led Tobirama to accuse the Sannin of planning to attack the village once again sending Hiruzen into outrage. Later admonishing his brother to be quiet as he spoke, Tobirama later chided the Uchiha clan openly to which Orochimaru contracted that it was Tobirama's fault it happened first place as he gave the Uchiha the Konoha Military Police Force to run and essentially ostracised the Uchiha. Rebuffing this, Tobirama explained the Uchiha clan's greatest curse: the fact that they had a greater love than any other person which if lost would turn into bottomless feelings of despair awakening the Sharingan as a result. He then explained that it was for this reason that he gave them that post so they would have something to focus their emotions on so that the world would not end up with a second Madara, who had suffered the loss of his brother whom he loved more than anything, on their hands.

Legacy
Tobirama's legacy in the ninja world at large, is mixed. He was known for building Konoha's infrastructure and revolutionising the ninja system on a whole by establishing organisations such as the Academy and ANBU, institutions and organisations adopted by most if not all of the Five Great Shinobi Countries as well as smaller ones. He also believed greatly in the Will of Fire and putting the good of the village above all else, beliefs which he passed on to the next generation.

Somewhat conversely, Tobirama set up the Konoha Military Police Force and assigned the Uchiha to it as a sign of trust. He in fact knew how unwieldy the Uchiha's emotions were and sought to have them focus their efforts of a single, constant goal all the while protecting the village as well. This in reality, however, actually became part of the Uchiha's demise as some came to see it as a means to ostracise them from the rest of the village and its governance and eventually led to the Uchiha Clan Massacre. Tobirama was also responsible for the creation of the Summoning: Impure World Reincarnation technique, which was used firstly by Orochimaru in his effort to destroy Konoha and later heavily relied on by Kabuto Yakushi during the Fourth Shinobi World War. Even though at the same time this had the reciprocal effect of having those that died with "unfinished business" as it were to settle them, the Fourth Kazekage and his son Gaara being prime examples. On a whole, Tobirama is still revered as a powerful shinobi and trail-blazing Hokage.

Trivia

 * means 'the space between two doors'. are seen as the access to progress and improvement which alludes to his role as the Hokage that built up Konoha's infrastructure. '扉' is also used to refer to title pages, tying in with the Hokage title, as a Hokage is as representative for the village as the title page is for a book.
 * Tobirama is a playable character in the Naruto: Ultimate Ninja series and in Shinobi Retsuden III.
 * Tobirama, along with Hashirama, Minato, and the Konoha symbol, had his face appear in the ending omake of Shippūden episode 129 within the fireworks.
 * According to the databook(s):
 * His favourite words were.

Quotes

 * (To Hiruzen) "Listen Saru. 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."
 * (To Hiruzen) "Saru, you must protect those who have faith in you and who love the village, and train up to those to whom you can entrust the next generation… from tomorrow, you will be the Hokage…!"