A long time after Inarius and Lilith had secretly created Sanctuary for the Nephalem who are the children of both man and Diablo IV Gold angel, the Council of Archangels convened to decide on humanity's fate. Tyrael was the one who cast the vote that decided the fate of humanity, and this means that he's responsible for his decision by the rest of the Angiris Council, leading to his death prior to happenings in Diablo 4 all for the for the sake of humanity. His role in the upcoming game is not yet clear however, there are possible ways that this key character will be considered in the future of Diablo.
Diablo 3 gets deep into Tyrael's tale, as he is transformed into The Fallen Star by tearing off his own wings and falling to Sanctuary where the descendants of the Nephalem dwell. As he joins forces with a powerful descendant, Tyrael defeats the primary evils and takes control over the Black Soulstone. After the Archangel of Death, Maltheal, went after the stone, and then became angry with all his followers and Tyrael was the one who took his friend to Pandemonium to end death itself.
Tyrael opts to stay in his mortal form . However, he reconnects with his angelic friends to transform into The Aspect Justice as well as of Wisdom. Diablo 3 ends with him wondering if his new mortal companion, who may be corrupted, will someday become the new danger for Heaven, Hell, and Sanctuary and even the very existence of life itself. Aspect of Justice and Wisdom Aspect of Justice and Wisdom likely won't sit idly by while Inarius marches an army upon Hell in search of his former love, Lilith.
The latest buy Diablo 4 Gold cinematic trailer from Blizzard showcases Inarius confronting Lilith, armies at both of their backs. While this scene lacks Tyrael's involvement directly, his creation of the Horadrim and the influence he has on the various Paladins of Sanctuary implies that he's definitely at work. Dark and light battles at the front, and the sadly dead Tyrael lies somewhere between.