A perfect being made as a weapon and pulled out of the cocoon too early, so he arrives as a very powerful child.
Adam Warlock is a perfect Sovereign created by Ayesha to destroy the Guardians of the Galaxy. He has the mentality of a child, because the High Evolutionary forced Ayesha to bring him out of the cocoon before he was ready in order to use him against Rocket.
That decision is the character. He is enormously strong and has no idea what he is doing, and Vol. 3 uses him as a study of what it is like to be made into somebody’s instrument, which is what the entire film is about.
Minor spoiler
Counter-Earth is destroyed and his mother is killed. Gamora captures him, he fails to kill Quill, and when the High Evolutionary abandons his own creations Adam saves Quill’s life instead. He joins the team Rocket assembles at the end.