The Mist Village Ninja (霧隠れ忍者, Kirigakure Ninja) is a team from the Naruto series created by Masashi Kishimoto. The series first began serialization in Shueisha's Weekly Shonen Jump in November 1999. It first appeared in Naruto Volume 2, CH. 9 "The Worst Client".
The Mizukage (水影, Mizukage) is the leader of the Mist Village. Only the most skilled and admired of the Mist Village Ninja are appointed to this position. They are responsible for governing and protecting the village and its people. It's unknown how they memorialize their previous leaders.
The Jōnin (上忍, Jōnin) are one of the highest class of ninja that can be obtained. On top of being the only rank of ninja to be given S and A Class missions, they are often also in charge of training squads of Genin-class ninja out of the academy.
The Chūnin (中忍, Chūnin) are the middle rank. They are appointed missions from C to B rank difficulties. The Chūnin are squad leaders.