Mū

was the of Iwagakure.

Background
During his lifetime, Mū taught his student Ōnoki how to use Dust Release. He also had a great enmity with the Second Mizukage. The two men eventually killed each other in battle.

Personality
Mū is an extremely calm and collected individual, showing no signs of perturbation to his sudden resurrection. He's also unfailingly polite, taking his time to recount the previous events to the other Kage upon their forced summoning, and referring to the one whom he both killed and in turn was killed by with an honorific title, apparently bearing no ill-will towards him.

Despite the seeming civility displayed towards his fellow Kage, Mū has demonstrated that he first and foremost prioritises the prosperity of his own village regardless of the manner in which this affluence is achieved, even reminding his disciple to take full advantage of any post-war situation to assure the dominance of Iwagakure by quickly seizing control of the resultant spoils. Even seconds before his sealing he attempted to warn Ōnoki to take precaution. This devious and somewhat merciless trait appears to be just one of the many reasons as to why the Second Mizukage despises him to such an extent.

Appearance
Mū's entire body is covered by intricately wrapped bandages, with only his eyes and nose being visible, giving him an overall mummy-like appearance. Along with this Mū wears a black headband with no distinguishing markings and a pair of black pants. He also doesn't wear shoes as his feet are also bandaged heavily. Due to the effects of the Summoning: Impure World Resurrection technique, he has black sclera and white irides.

When he was still alive, Mū was shown to have donned what appeared to be a standard Iwagakure's flak jacket, with the village distinctive single sleeve outfit over his left arm. He also carried two swords strapped to his back which had slender handles and were also bandaged.

Abilities
Having been the Kage of his village, Mū is an immensely powerful shinobi. He 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. While alive he carried a pair of what resembles swords wrapped up in bandages.

Mū is a skilled sensor-type shinobi displaying the ability to sense chakra over a distance of several kilometres, as well as to discern the similarity between the chakra belonging to close relatives such as Gaara and his father, and distinguish chakra from different populations. Furthermore, when these detection capabilities are employed in conjunction with his quick reflexes, he can avoid techniques that even other Kage find difficult to evade, as demonstrated when only he instinctively managed to elude the clutches of Gaara's hands made from sand and avoid Naruto's attack from behind. He has also demonstrated the capability to levitate and fly, as well as being able to split himself into two duplicates to help escape a lethal blow, but at the cost of reducing his power by half. He was also physically strong enough to lift massive rocks off of his body.

Invisibility
Mū is capable of becoming perfectly camouflaged with the surrounding environment. His camouflage is so good that he has become renowned as the, a title which he gained for seemingly having neither form nor chakra, while the technique was active. It is impossible to detect him by normal means and so, Mū considers anyone with the ability to sense his presence worthy of praise.

Nature Transformation
Mū is one of the few people capable of using a kekkei tōta, an advanced and extremely powerful form of kekkei genkai. In particular, he possesses the Dust Release, which allows him to combine the fire, earth and wind natures to reduce his opponents to nothing more than mere dust, destroying them down to even a molecular level. Compared with fellow dust-user, Ōnoki, his power is implied to be on equal terms, as when the two initiated Dust Release: Detachment of the Primitive World Technique, the disastrous outcome although chaotic, demonstrated no evident victor in regards to strength. This may be due to the fact that Mū's power hadn't waned since his lifetime, a fact later affirmed by even Ōnoki.

This Dust Release makes him so powerful that the Allied Shinobi Forces fear him greatly, and Ōnoki only trusts himself to fight him, an assertion which Tsunade agrees with. Mū himself declares that sheer numbers alone do not matter in the face of his techniques, in spite of confronting nearly the entire Fourth Division at the time.

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 mobilised, 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. Recognising the means of their revival as the Impure World Resurrection, Mū searched for the Second Hokage, the technique's inventor and thus the presumed user, but informs his comrades that he could only pick up the presence of someone whose chakra signature was similar to the Fourth Kazekage's, and that that person is backed by a large army. The Fourth Kazekage then explained that the Second Hokage had been dead for many years, while also declaring that the one known as Orochimaru knew the deceased Hokage's technique as well. Mū later notifies the Second Mizukage that they're being controlled and thus, some of their movements are restricted, much to the latter and the Raikage's dismay.

Pursuing the division throughout the entire night alongside the others, he remarks that their intended targets had been slowly retreating due to their indecision but that the opposition's movements have now altered, concluding their pursuit. When the Second Mizukage laments upon the prospect of confronting shinobi from his own respective village and curses the one responsible for resurrecting them, even Mū is in agreement. Shortly after, he detects the approach of two individuals, who are preceded by a colossal wave of sand that bears down on the four. However, the Fourth Kazekage swiftly counteracts this through his Gold Dust. At this point, Gaara appears suspended above them and summons hands of sand to ensnare the Kage, with only Mū being able to escape captivity while sensing Ōnoki's presence above, who appears to have lived a long life thanks in part to his master's teachings. Utilising the same technique to repel that of his former disciple, the converging attacks result in the formation of a huge crater in the middle of the battlefield, leading Ōnoki to assert that his predecessor's strength hadn't waned at all.

Suspecting a shinobi alliance had been formed, due to the accumulation of chakra types from different villages, Mū remains surprised that such a merger has occurred when it is later affirmed by Ōnoki. Informing his former disciple that only he can stop him, Mū then reminds Ōnoki that by taking full advantage of the post-war situation, the dominance of Iwagakure can be assured. Offending the Second Mizukage, the Third Raikage and most shockingly Ōnoki with such devious tactics, Mū immediately isolates himself when the battle resumes, pursued only by the latter. As the chase concludes, with both men seemingly clashing several times, Mū declares to a visibly exhausted Ōnoki, that his age had caught up to him and as he disappears from view, to call Gaara before he died too. However, telling Mū not to underestimate him just yet, Ōnoki creates several clones.

As their battle ensues, Mū takes Ōnoki by surprise from behind in mid-air yet due to Gaara's arrival and timely warning, Ōnoki manages to aviod the blow while seemingly throwing his back out in the process. Preparing to attack them with his Dust Release, Naruto attempts an ambush with his Planetary Rasengan but sensing the attack, Mū easily evades it. Believing his technique to be the faster, only the combined efforts of both Gaara and Naruto ensure that the latter lands a hit on a shocked Mū, sending him hurtling through a nearby outcrop. Colliding with the ground below, Ōnoki swiftly moves in and turns his body to stone, preventing him from moving.

As Mū is being sealed within Gaara's sand, he tells Ōnoki that for someone who detested other villages, he worked well with them to which Ōnoki replies that he had lived long enough to experience such a change. Just as the seal nears its completion, he says "Be careful, I…" but is completely sealed before he can finish his statement. Some time later, whilst unearthing himself from the nearby rubble left in the wake of Naruto's devastating attack, a damaged but regenerating Mū, chastises his former disciple for still being naive, having overlooked his body splitting while it was obscured by Naruto's attack. Unable to remove the seal that bound his other half, Mū is forced to await Kabuto's instruction, until the preparations for "that" summoning are concluded. After more time passes, Mū performs the Summoning Technique.

Narrowly avoiding the fragmented lid after it is violently removed from the resulting coffin, Mū looks on in shock at the shadowy figure who emerges, remarking that the individual behind their resurrection must have a good understanding of war to summon such a person. Together the pair walked to Ōnoki and Gaara's location, where it is revealed that the one Mū summoned is Madara Uchiha.

Trivia

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