While Avengers: Endgame was an adaptation of a Marvel comic book series known as the Infinity War saga, it wasn’t a very faithful one. Possibly the biggest deviation from the storyline that the film has though is the absence of Adam Warlock, a cosmic being in the MCU whose presence has already been hinted at in Guardians of the Galaxy Vol. 2.
In the comics, he played a crucial role in the Infinity War saga as he was the wielder of the Soul Gem and a former ally of Thanos who turns on the Mad Titan after learning of his evil plans. Adam Warlock was also the man who wielded the Infinity Gauntlet containing the six stones of power to undo the damage wrought by Thanos’ hand.
So, why was he left out of the film? Well, during an interview for Backstory Magazine, scribes Christopher Markus and Stephen McFeely explained why such an important character wasn’t included, saying:
The logic right here was to honor the MCU as how it had already existed and the characters you’d already fallen in love with. We did not want to give too much story space to introducing a whole new person. It would rob you from somebody. We were doing the Black Panther thing with a brand-new cosmic character in the form of Captain Marvel. Her movie had not really even been conceived yet, so to bring her in as an even more cosmic character made sense.
So, it seems that a surfeit of important heroes that already exist in the MCU is the reason why fans didn’t get to see Adam Warlock as well. The writers’ decision makes sense, too, since Avengers: Endgame already had more protagonists and a bigger supporting cast than any other movie in history. If Warlock had also been included, he would’ve either had a very brief cameo that shortchanged his character or would’ve stolen precious screen time away from other heroes who’ve been a part of the MCU for the past decade.
Choosing Captain Marvel to be the alien outsider who comes in to lend a hand to Earth’s Mightiest Heroes instead feels more organic, considering her close ties to Nick Fury and her character having already received an entire movie to explain her origin to the audience. But Adam Warlock’s time to shine is surely coming soon, as the MCU will continue to expand into the more cosmic realms of the franchise as we move into Phase 4 and beyond.