Gengetsu Hōzuki

He was the of Kirigakure.

Background
The Second Mizukage was killed by the Second Tsuchikage. However, before his death he was able to kill the Tsuchikage too.

Abilities
Though so far he has not been seen in combat, the fact that he was able kill to Mu, who the Shinobi Alliance fear no one but Onoki could stop (albeit also dying to Mu in the same battle), suggests his combat capabilities are truly fearsome.

Shinobi World War Arc
Mū, as a former Kage, is resurrected alongside various other notable shinobi by Kabuto Yakushi, in preparation for the Fourth Great Shinobi War. He, the Third Raikage, and the Fourth Kazekage are sent to provide backup for the Second Tsuchikage in fighting the Fourth Division. Although he wants to try and kill the Tsuchikage again, he is forced to join the others in battle.