Mizukage

The is the leader of Kirigakure. As the official head shinobi of Kiri, his word holds sway over all political and militaristic issues that present themselves regarding Kiri and its villagers.

Madara Uchiha
The only named Mizukage that has been introduced so far in the series is Madara Uchiha, though it's unknown when he gained the title of Kage and how many Mizukage came before and after him. It has been confirmed that Madara is not the current Mizukage. Nothing has been revealed about his time as the Mizukage.

Deceased Mizukage
Five years prior to the start of the series, Zabuza Momochi lead a group of Mist ninja to assasinate this Mizukage and take over Kiri. Though Zabuza suceeded in killing the Mizukage, he ultimately failed to pull a complete coup d'état and retreated out of Kiri with few remaining subordinates. The gender of this Mizukage is unknown.

Current Mizukage
In the Eight-Tails arc, the current Raikage of Kumogakure demanded a meeting of the five Kages to discuss the problem of the Akatsuki. Whoever the current Mizukage is, he/she will make an appearence at the meeting.

Arguments
It Wasn't confirmed that he wasn't the mizukage no more...To my point of view he's still mikukage, when madara is talking to kisame, Chap. 404-pg.2 Kisame states: "I'm relieved...It'll be easier for me to do my work with you pulling tha strings mizukage...I mean, Madara". [to my point of view he is talking about the present, so he's still mizukage..:O?]

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