Venom

Played by Tom Hardy

Venom is the alien symbiote bonded to Eddie Brock, one of a race of amorphous creatures from the planet Klyntar that Knull created to serve him before they turned against their maker and imprisoned him. Given a voice and a personality distinct from Eddie's, Venom is violent, sardonic, and fiercely possessive of its host, professing to love him even while arguing with him constantly. It ultimately sacrifices itself, destroying the Codex -- the genetic key that could free Knull -- and dies keeping him contained. Read more →

First turns up in Spider-Man 3.