Mizukage

The is the leader of Kirigakure. There have been six official Mizukage and their word holds sway over all political and military issues that present themselves regarding Kirigakure and its inhabitants. The Mizukage's building is the widest and largest landmark in Kirigakure, bearing the kanji for on it.

Fourth Mizukage
He was manipulated by Tobi who could be called the "real" Fourth Mizukage.

Trivia

 * Unlike the other five Kage, there is no sort of connection between the Mizukage. Instead, the Mizukage position is filled by the strongest person in the village. This can lead to cases where very young people become Kage, such as the Fourth, Yagura.