Marvel movies are infamous for the plethora of characters rumored to appear, might appear, or almost appeared. It's gotten worse since the films went cosmic, and the one character mentioned the most is Adam Warlock, the number of rumors about him are so many they even be too much for the perfect being to calculate. He was reportedly very close to being in Guardians of the Galaxy Vol. 2, and now Avengers: Infinity War writers say they almost made him part of the already jam-packed film.
Writers Stephen McFeely and Christopher Markus tell Entertainment Tonight the reason Adam Warlock wasn't part of the 200+ Infinity War characters (give or take a few) is because he's just got too complicated of a history. That's putting it mildly, and rather than explain it you should just read this.
Markus said, “We didn’t introduce Adam Warlock, because it’s a massive backbend and you practically have to make an Adam Warlock movie to introduce him. He just can’t walk onscreen. So, there was a brief moment where we were like, Ehhh…, and then we were like– [He points to the movie’s poster.] We have that many characters already! And then there were others we couldn’t use. Like, Silver Surfer would have been useful, but we can’t touch him. Currently.”
I like that hopeful "currently" he adds at the end there.
So nope, no Adam Warlock, and I think that was a smart idea. Adam Warlock is such a huge force in the cosmic corner of the Marvel Universe that he really does need a movie of his own. However, we have seen various teases of him in both Guardians of the Galaxy movies so somebody at Marvel is preparing us for Warlock's arrival.
