Nebula was first introduced in the Marvel Cinematic Universe through Guardians of the Galaxy. She was an antagonist alongside her “sister” Gamora, another child of Thanos. Nebula had quite a powerful arc from Guardians 1 and Guardians 2 to Avengers: Infinity War and Avengers: Endgame. As Karen Gillan teased before Endgame, fans ended up rooting for Nebula. She and Rocket ended Infinity War as the last two Guardians standing. The Nebula of Avengers: Endgame‘s present killed her own 2014 counterpart, but by the nature of Endgame‘s time travel rules, that didn’t launch a universe-shattering paradox or anything like the fears from Back to the Future.