Indoril Nerevar was the Chimeri king of Resdayn (modern-day Morrowind), a war hero who united his people, and the founder of House Indoril. He became the Herald of the Tribune Way, and as such is the foremost of the saints of Dunmeri faith, along with his wife, blessed Almalexia the Warden, Lord Sotha Sil the Magus, Lord Vivec the Poet, and Saint Veloth the Pilgrim. Prophecies of his "rebirth" as the Nerevarine and heroic return to Morrowind fueled the creation of the Nerevarine Cult. He possessed the Dwarven artifact Moon-and-Star, a ring which lent him supernatural powers of persuasion; because he was the only person who could wear the ring, it also became a means to prove the identity of the Nerevarine.
Together with Dumac Dwarfking, Indoril Nerevar forged an alliance between the warring clans of Chimer and Dwemer in 1E 401 against Skyrim invaders. Although this alliance faced many challenges and suspicions, it finally succeeded in pushing the Nords out of Resdayn by 1E 416. This wartime alliance developed into the First Council, securing an uneasy peace. Resdayn flourished under the leadership of Dumac and Nerevar. Peace among the Chimer, and between the elves and the dwarves, brought an unprecedented prosperity and flowering of both cultures.
Nerevar was killed during or shortly after the Battle of Red Mountain, under disputed circumstances. He is said to have killed Dumac, the Last Dwemer King. In some versions, he rejoiced in the deed, and feasted on his heart: in others, Dumac and Nerevar had been allied, and the betrayal (by Dumac's minion Kagrenac), which led them into conflict, grieved both Nerevar and Dumac greatly.
In Ashlander texts as well as accounts by the Dissident Priests found in Vivec's temple, however, it is written that Nerevar was not killed in combat, but by his three advisors, Vivec, Almalexia, and Sotha Sil. In this account, Nerevar made them swear to never use the tools, and they obeyed, but secretly conspired to murder Nerevar so that they might gain power. When attempting to summon Azura, Nerevar was foiled; Almalexia used poisoned candles and Sotha Sil used poisoned robes and Vivec used poisoned invocations. Nerevar was killed. In retribution for their betrayal, Azura turned the skin of the Chimer gray, and turned their eyes fiery red. However, the Tribunal (that is, Vivec, Almalexia and Sotha Sil) went on to use the power of the tools and the Heart to become immortal. Afterwards, they set themselves up as the new gods of the Dunmer, claiming superior divinity to the Daedra, for whose worship the Dunmer had exiled themselves. Eventually, their Tribunal Temple took control of all of Morrowind, becoming the monolithic and seemingly infallible entity it was by the end of the Third Era, and leaving only isolated pockets of Ashlanders to maintain the old beliefs.
Azura herself corroborates the oath taken and broken by the Tribunal. For their treachery, Azura proclaimed that someday Nerevar would be reincarnated and would make things right again. This led to the persecution of followers of the Nerevarine Cult. However, Azura accused them of betrayal, she never implicated them in Nerevar's murder. At the time the Tribunal received the tools, they only knew their use had caused an entire race of Mer to vanish, so had no reason not to agree to Nerevar's oath in good faith. Both Vivec and Almalexia claim that it was only after years of Sotha Sil's research they understood how the tools could be safely used, and the chronology of their visits to Ash Mountain and the assumption of their divinity support this claim.