He is the Second Tsuchikage.
Before becoming the Second Tsuchikage, he accompanied the First Tsuchikage to the first ever Five Kage Summit. There he stood behind the First watching diligently as the proceedings unfolded.
During his lifetime, Mū taught Ōnoki how to use Dust Release. At some point in time, both he and Ōnoki met with Madara Uchiha, after an alliance had been formed between their respective villages. Despite their standing, Madara boldly declared that Konohagakure would remain the dominant power and as such, they should obey any orders given. This culminated in both parties engaging in battle where Mū and Ōnoki were defeated. It was during Mū's era when Iwagakure began to actively try to acquire other tailed beasts, having the Four-Tails and the Five-Tails already in its possession.
He also had a great enmity with the Second Mizukage and the two men eventually killed each other in what would be their final confrontation.
In preparation for the Fourth Shinobi World War, Mū was reincarnated by Kabuto Yakushi alongside three other deceased Kage to fight against the Allied Shinobi Forces. When they were mobilised, Mū was sent in the direction of the Fourth Division but despite being invisible as he approached their location, he was detected by Gaara — a feat which he commended as he was forced to summon the Third Raikage, the Second Mizukage and the Fourth Kazekage. After a brief argument with the Mizukage over the manner of their deaths, Mū noted the means of their reincarnation, and searched for Tobirama Senju, believing him to responsible for their return before informing his fellow Kage that he could only pick up the presence of someone whose chakra signature was similar to that of the Fourth Kazekage's and that, that person was backed by a large army. The Kazekage then explained that Tobirama had been dead for many years during his lifetime and that he knows another who can use the deceased Hokage's technique as well. Mū and the other Kage pursued the division throughout the night, forcing their opisition into a slow retreat until cornering them.
Mū VS Ōnoki The results of Ōnoki and Mū's battle. He then detected two individuals approaching, who are preceded by a colossal wave of sand that bore down on the Kage, but the Fourth Kazekage swiftly counteracted this with his Gold Dust. At this point, Gaara appeared suspended above them and sculpted hands of sand to ensnare the Kage, with only Mū able to escape captivity while sensing Ōnoki's presence above them. Greeting his old pupil he noted that Ōnoki had lived a long life thanks in part to him passing down his teachings to him. Utilising the same technique to repel that of his former disciple, the converging attacks resulted in a huge crater in the middle of the battlefield, leading Ōnoki to assert that his predecessor's strength hadn't waned. Suspecting a shinobi alliance had been formed due to the accumulation of chakra types from different villages, Mū was even more surprised that such a merger has occurred when it was confirmed and even more so that Ōnoki had joined it. Informing his former disciple that only he could stop him, Mū reminded Ōnoki that by taking full advantage of the post-war situation, the dominance of Iwagakure could be assured. Offending the Mizukage, the Raikage and most shockingly Ōnoki with such devious tactics, Mū immediately isolated himself when the battle resumed, pursued only by his student.
Mu defeated Mū is struck by Naruto's Planetary Rasengan. As the chase concluded after the pair had seemingly clashed several times, Mū declared to an exhausted Ōnoki, that his age had caught up to him and as he disappeared from view, and told him to call Gaara before he died as well. However, telling Mū not to underestimate him just yet, Ōnoki creates several rock clones. As their battle ensues, Mū took Ōnoki by surprise from behind in mid-air, but with Gaara's timely arrival and warning, Ōnoki managed to avoid the blow but threw his back out in the process. As Mū prepared to attack them with his Dust Release, Naruto Uzumaki attempted an surprise attack with his Planetary Rasengan technique, but, sensing the attack, Mū easily evaded it. Believing his technique to be the faster of the two, only the combined efforts of both Gaara and Naruto ensure that the latter lands a hit on a shocked Mū, which sent him hurtling through a nearby rocky outcrop. Colliding with the ground below, Ōnoki swiftly moved in and weighed Mū's body down, which prevented him from moving.
Mu's emerging Mū's other half emerges from the rubble. As Mū was being sealed within Gaara's sand, he told Ōnoki that for someone who detested other villages, he worked well with them, to which Ōnoki replied that he had lived long enough to experience such a change. Just as the seal neared its completion, Mū attempted to warn them but was sealed in full before he could finish his sentence. The warning was revealed when Mū emerged from the rubble left in the wake of Naruto's devastating attack. Chastising his former disciple's naivety as his wounds heal, Mū reveals that he split his body into two while it was obscured by the prior attack. Unable to remove the seal so he could reunite with his other half, Mū was made to begin summoning "that" reincarnation. Due to his weakened state, it took longer for Mū to complete the summoning. In the anime, it took so much time, Kabuto was required to summon various additional reincarnations to stall.
Fourth Shinobi World War: Climax Edit Mū summons Madara Mū summons Madara. Eventually, Mū completed the Summoning Technique. Narrowly avoiding the summoned coffin's lid after it was violently blown off, Mū was shocked at the figure who emerged, remarking that the individual behind their reincarnation must have a good understanding of war to summon such a person. Together the pair walked towards Gaara and the Fourth Division, where it was revealed that the one Mū summoned was Madara Uchiha. When Madara noted that all of the shinobi were wearing similarly marked ("shinobi" (忍)) forehead protectors, Mū informed him that an alliance had been formed in response to the on-going war. As Mū was unable to answer Madara's question about who was controlling them, Kabuto overrode Mū's consciousness and used him to talk directly with Madara. As the battle restarted, Mū narrowly avoided Gaara's attack, and attempted to form a Dust Release technique, but it soon dispersed due to his power in his split state. Observing the ensuing conflict, Kabuto continued to speak through Mū's where he remarked upon Madara's demonstration of the Rinnegan and its power, even after the impact of two enormous meteorites.
Mū departing Mū's soul begins departing. Reforming in the wake of the collision, Kabuto had Mū approach the few remaining survivors of the Alliance, whilst providing Madara with a detailed overview of current affairs. However, when the two resumed their attack, they are repelled by Tsunade and A who had just been transported to the battlefield. Recovering from A's punch, As Mei created a thick mist, obscuring the battlefield, Kabuto positioned Mū right in front of Madara but he was easily knocked away by a lightened A. Afterwards, Mū was pursued by Dodai and the Hokage Guard Platoon. Once recovered, Mū continued to elude his pursuers under Kabuto's direction, as the battle between Madara and the Kage intensified. Later, with the Impure World Reincarnation being released, Mū's consciousness returns to him but only for a short while as he was enveloped in a light of sorts and began deconstructing, much to his shock, regaining his consciousness only mere moments before starting to break down and his soul returned to the afterlife. In the anime, before his soul ascends, Mū told his opponents to tell Ōnoki that he must protect the future of the Shinobi Alliance and only then can he come and tell him all about it.
Kaguya Ōtsutsuki Strikes Edit Combined Kage summoning The deceased Kage summoning Team 7 and the tailed beasts. Subsequent to Kaguya Ōtsutsuki being sealed by Naruto Uzumaki and Sasuke Uchiha, he and the other deceased Kage were summoned from the Pure Land by Hagoromo Ōtsutsuki to aid him and the Hokage in summoning Team 7, the tailed beasts and Madara from Kaguya's dimension. Later, his and the other Kage's souls were returned to the Pure Land.
He possesses the Kekkei Tota. Simultaneous activation of three Chakra Natures Wind, Earth, and Fire. He was the one that taught Onoki Particle Style.
Chakra Nature: Lets start with the basics. The properties of Chakra. Generally we all posses one Chakra Nature. Besides the Nature we obtain from training that is. There are different Chakra Natures. The more Chakra Natures you have the better. That's why most Jounin posses multiple Chakra Natures. However some shinobi are different they are born with two Chakra Natures. They are able to fuse those two Chakras and by doing so create a new Chakra. They are known as Kekkai Genkai Shinobi.
Lord Mu was able to split his body and in doing so he created Clones. Well no, not Clones, its closer to say that he splits his body into two pieces. Although each one only has half his normal strength.