Nebula is a fictional character appearing in the Marvel Cinematic Universe, prominently featured in 'Avengers: Endgame.' She is a skilled warrior and the adopted daughter of the intergalactic warlord Thanos. Initially depicted as a villain, Nebula undergoes significant character development throughout the series. In 'Endgame,' she plays a critical role in the Avengers' quest to undo Thanos' devastating actions. Her journey involves reconciling with her sister Gamora and ultimately fighting alongside the Avengers, highlighting her evolution from a tortured antagonist to a reluctant hero with a complex moral compass.