Marvel Heroes Villains
Venom
Venom had a strange beginning in comics. He was part of a race of symbiotes from the planet Klyntar. These beings merge with hosts, and the combined entity tends to have a personality based on both the symbiote and the host itself, though sometimes one side or the other tends to dominate.
During 1984's "Secret Wars" Spider-Man aquired a special costume after his was destroyed. This costume turned out to actually be the symbiote that would become Venom. The costume eventually began taking over Spider-Man and had to be removed, with help from Reed Richards of the Fantastic Four.
There have been two Sony films starring Tom Hardy portraying Venom. Both have been hits but are not a part of the Marvel Cinematic Universe. That somewhat changed with a post-credit scene of Venom in the "Spider-Man: No Way Home" movie. Maybe we'll see Spider-Man fight Venom yet in a "good" film. Fingers crossed.