Adam Warlock is one of the most powerful heroes in the entire cosmos. We can definitely expect to see him in the Marvel Movies. His first appearance in the comics was in Fantastic Four #66. But after he was teased in Guardians of the Galaxy 2 there have been rumors going around that he going to make an appearance in Guardians of the Galaxy 3.
The Arch-nemesis of Thanos was first rumored to get a debut in Avengers Endgame. But the Marvel Studios people have confirmed it that he is not a part of the movie. This rumor started mainly because in the comics, Adam Warlock is the one who kills Thanos or more like tricks Thanos into killing himself.
Adam Warlock has only been teased in the post-credits of Guardians of the Galaxy 2. Ayesha, the main villain of the movie, was shown naming the man who will be out of her birthing pod as “Adam”. She swears revenge upon the guardians in the post-credits scene. She described him as the one who is “capable” of destroying the Guardians of the Galaxy.
In the comics, Adam Warlock is an alien born from a cocoon. He is a villain at the beginning of his debut. A synthetic being created by human scientists called “The Enclave”. They created him to become their ideal template for a new race of humans who would one day rule the Earth.
In the MCU, while Warlock was originally created with evil intentions in mind, he has carved out a heroes life for himself. His origin has changed a bit. He is now created by the sovereign instead of the Enclave. He was made to kill the Guardians of the Galaxy. Will he do so, or like his comic book counterpart, will he break against programming? We’ll have to wait and find out.
HIS ORIGIN:

Early in his existence, Adam Warlock had a soul gem giving him 1/6th of the infinity gauntlet’s power. He had a villain called Magus and in the battle, he allied with Gamora, Pip the Troll, and Thanos. He then discovers that Magus is no one else but his future self and he decides to kill himself before he can become Magus.
When Thanos turns on Warlock, Warlock discovers that he has the ability to regenerate from a cocoon. He plays a key role in defeating Thanos in Infinity Gauntlet.
Now even though there is no other information that confirms Adam Warlock’s approach in Guardians of the Galaxy 3, there is a high chance that he is going to join the team as he is one of the most powerful characters in Marvel Comic. Therefore he will definitely be needed in Phase 4 which is going to adapt the Secret Wars onto the Big Screen.