Venom is a antihero and supervillain in The Amazing Spider-Man comics by Marvel. Venom is an extraterrestrial symbiote in many of its incarnations, with the exception of the Ultimate Spider-Man television series, where Venom is created from Peter Parker's blood and while still a symbiote, is not alien.
Venom's first host was Peter Parker, who later rejected Venom. The symbiote then bonded with Peter's rival Eddie Brock and the two set out for revenge on Peter, who Eddie now knew was actually Spider-Man. Other known hosts of the Venom symbiote are Mac Gargon the Scorpion, Flash Thompson, who was known as Agent Venom, etc.
The cinematic incarnation of Venom who appears in Spider-Man 3 follows the storyline of the comics where it first bonds with Peter Park and later Eddie Brock, though this incarnation is widely criticized over the character's lack of screen time and the supposed mediocre performance of Brock's actor Topher Grace.
Venom also appears in his solo movie where he again bonds with Eddie Brock. (both played by Tom Hardy)