Mizukage

The is the leader of Kirigakure. There have been five official Mizukage, though the Third has not been seen in the series thus far. 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

 * The Second Mizukage is seemingly the only Second Kage to not have been in attendance at the first gathering of Kage.