Byakuren

The was the one who founded Kirigakure in the Land of Water.

Background
At the first meeting of the five Kage, accompanied by a shinobi from his village, he sat alongside the others and told Hashirama Senju that if he acted so humbly as to bow to them, his equals, he would suspect something was wrong. He later expressed outrage when the First Kazekage made a demand that instead of receiving a tailed beast as the sand priests had already sealed away one, they requested 30% of whatever they would pay for a tailed beast from Konoha, claiming the amount to be too high a demand. As infighting broke out and Hashirama made his plea to them to preserve the future of their children and unite, he looked on somewhat disapprovingly at the proceedings.

Personality
While much was not seen of his personality, he seemed to be cautious in nature while being a frank person, mincing no words with the First Kazekage when he showed no signs of lowering or abandoning his conditions for signing the treaty, and noting that if Sunagakure were to plan to attack them, the other nations could band together and destroy them. His cautious nature was also displayed with Hashirama when the latter was acting too humble over the five Kage meeting for his liking, going as far as suggesting that Hashirama had a hidden agenda for the meeting.

Appearance
In his old age, the First had long, unkempt hair, beard, and mustache that covered almost the entirety of his face. He had a scar that ran down the left side of his face and across his left eye, in which he was seemingly blind. His teeth were sharp and triangular; a trait carried by generations of shinobi from Kirigakure. Attire-wise, he wore a simple, light-coloured, loose-fitting kimono.

Abilities
As the First Mizukage and the founder of Kirigakure, the First Mizukage was undoubtedly an extremely powerful shinobi.

Trivia

 * The First Mizukage was the only one who seemingly attended the first gathering of the five Kage without his successor.