Every Blizzard game since WarCraft 3 (maybe even Diablo) has been: “THE PROPHECY IS COMING TRUE! Listen to this prophet who was seen as a bad guy in previous game, but is now Team Good Guys because the world will end!” Medivh, Zeratul, and Tyreal/Caine/Adria. You have to stop the Burning Legion/Amon/Prime Evils.

I haven’t played Overwatch, but I bet it’s the same plot.