Mizukage

The is the Kage of Kirigakure, a title bestowed on the village's leader. The Mizukage is generally regarded as the strongest shinobi in the village. There have been six Mizukage in the village's history.

Overview
The Mizukage position was created after the formation of Kiri by Byakuren, the village's founder, that in anime was the fourth of the five Kage to emerge. The position is filled by the strongest person in the village, regardless of considerations such as age. The Mizukage's building is the largest landmark in Kirigakure, bearing the kanji for on it.

Throughout history, the word of the Mizukage has influenced all political and military issues that arise in relation to Kiri and its inhabitants, with each of the first four leaders having their governments mainly marked by strong secrecy, strict internal politics and limited interaction with other villages. It was not until the reign of the Fifth Mizukage that the traditional governance of the position would undergo a reform which would restore diplomatic relations with other villages.

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

Trivia

 * Due to Obito Uchiha using genjutsu to take control over Yagura Karatachi, he is effectively considered the true Fourth Mizukage, as Kisame Hoshigaki referred him to as such.
 * Mizukage are the only Kage not known to be related by blood to one another.