Mū

was the of Iwagakure and the sensei of the Third Tsuchikage, Onoki.

Appearance
It appears that the entirety of Mū's body is covered by intricately wrapped bandages, with only his eyes and nose visible, giving him an overall mummy-like appearance. These features are accentuated by a dark colored headband with no distinguishing markings and black shorts. Due to the effects of the Summoning: Impure World Resurrection technique, he has black sclera and white irides.

Abilities
Mū has been observed utilizing an ability that allows him to become perfectly camouflaged with the surrounding environment, similar to other Iwagakure shinobi. It is hinted by statements that he himself has made, that detecting not only his movements but also his presence is no easy task and thus something worthy of praise. This is confirmed when the Shinobi Alliance's Sensor Division couldn't sense Mū at all.

He also appears to be both extremely knowledgeable and analytical, being able to discern the exact method used to locate his position almost immediately after detection, seemingly without any prior information concerning the technique in question.

Mu also is a a user of the kekkei tōta Dust Release which allows him to control Fire, Earth and Wind style jutsus.

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. When the Kage are mobilized, Mū is sent in the direction of the Fourth Division. As he approaches their location invisibly he is detected by Gaara's Sand Sensing technique, something which he commended his opponents for achieving.

Upon being noticed, Mū was forced to summon the Third Raikage, the Second Mizukage, and the Fourth Kazekage. As Mū and the Second Mizukage conversed, confirming their mutual death at the other's hand, Mū explained that they were summoned by the Second Hokage's Impure World Resurrection technique, but also made note that he couldn't sense the Second Hokage anywhere, mistakingly believing that he had summoned them. The Fourth Kazekage then explained that the two had been dead for "many, many years", while also explaining that the one known as Orochimaru knew the Second Hokage's technique as well. While conversing with the other Kage, Mū noted that the summoning technique limited their actions, because despite the mutual desire to kill the Second Mizukage (again), his body wouldn't move.

Trivia

 * can mean nothingness or non-existence; possibly alluding to his ability to become invisible.
 * His appearance and the technique he uses may be referring to the main character of "The Invisible Man" novel of H.G. Wells.