After seeing his son's failure as Venom, the Goblin took a sample of the Symbiote and modified it. When the time came to give the symbiote it's host, he chose Peter Parker(Ultimate Spider-Man), claiming a "wimpy kid" would appreciate the symbiote's gifts, unaware that Peter was, in fact, Spider-Man. The Goblin captured Peter and injected the symbiote directly into his bloodstream, giving it a red discoloration. Upon bonding with Peter, the symbiote took control of his body and began destroying the Goblin's lab, eventually being subdued by the Goblin. Inspired by the destruction it had created, the Goblin named the creature "Carnage".
Carnage was sent to attack the S.H.I.E.L.D. Trainees and bring Spider-Man to him, still unaware the Peter was the wallcrawler. Carnage very easily defeated the teenage heroes, and was only stopped when Harry Osborn intervened.
Due to the Venom symbiote still being present within the Carnage symbiote, Harry was able to call the symbiote to him, freeing Peter and becoming Venom once more. However, the combination of the Venom and Carnage symbiotes allowed Harry more control.