Mizukage

The is the leader of Kirigakure. As such, their word holds sway over all political and military issues that present themselves regarding Kiri and its inhabitants. Zabuza Momochi once tried to assassinate a Mizukage as part of a coup d'etat, but failed.

Unknown Mizukage
At some point in time, Madara Uchiha was made Mizukage as he was recognized as such by Kisame Hoshigaki. It is unknown which number he had.

Current Mizukage
The Current Mizukage is a young woman and it is suggested that she has only just become Mizukage. It is unknown which number she is.