His role in the coming game is unclear at present however
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After Inarius and Lilith secretly created Sanctuary with Diablo IV Gold the Nephalem as the children born to both man and angel, the council of Archangels met to decide humanity's fate. Tyrael was the one who cast the decisive vote, as such, he'd be held responsible for that decision by all of the Angiris Council, leading to him becoming mortal prior to any events in Diablo 4 all for the good of mankind. His role in the coming game is unclear at present however there are likely ways this pivotal figure will be considered in the future of the series.
Diablo 3 gets deep into Tyrael's saga, as he is transformed into The Fallen Star by tearing off his own wings before falling into Sanctuary where the descendants of the Nephalem are residing. When he is joined by a powerful descendant, Tyrael defeats the Prime Evils and takes the control of the Black Soulstone. After the Archangel of Death, Maltheal, went after the stone and took on all of his companions It was Tyrael who was the one to send his friend into Pandemonium to destroy death itself.
Tyrael prefers to retain his mortal form . However, he joins his angelic brethren to transform into his Aspect Justice and of Wisdom. Diablo 3 ends with him thinking about whether his mortal counterpart, who is likely to be corrupted, could be the new danger of Heaven, Hell, and Sanctuary and MMoexp.com even the life itself. There's a reason that Aspect of Justice and Wisdom is likely to not sit idle while Inarius takes on an army of Hell to find his old love, Lilith.