Hashirama Senju's statue at the Valley of the End
Hashirama was originally the leader of the Senju Clan of the Forest. At some point in his life he fought Kakuzu but the nature of this fight is unknown at this point.
During the first wars he and the Senju Clan constantly fought the Uchiha Clan and he himself Madara Uchiha personally, even to the point that when someone hired the Senju Clan, the opposing part would hire the Uchiha Clan, and vice-versa. He and his clan offered a truce with the Uchiha Clan and allied with Madara Uchiha, and the two of them, with their clans, founded Konohagakure.
Later on, Madara left the village because during the times of peace, he was called a monster by his clan, saying that he took his brother's eyes for his own selfish desires, when they were given to him freely in order to protect the clan. This conflict resulted in the battle with, and defeat of, Madara Uchiha and the nine-tailed fox at the Valley of the End.
To commemorate the battle, two statues, of Madara and Hashirama, were carved into the earth around the waterfall. It is for this reason that Naruto Uzumaki and Sasuke Uchiha's fight at that location was noted to be ironic.
At some point he would gain control of several Tailed Beasts, that he would later spread out between the nations, as the peace talks were happening, and in order to equalize the powers between the nations.
However the war still waged on, and thinking about the future of Konoha, he and his younger brother, the future Second Hokage, trained the young Sarutobi, the future Third Hokage. However, long after founding Konoha, Hashirama died in battle, leaving behind his younger brother who inherited the Hashirama's title and thus became the Second Hokage.
