Carl Mach was a volunteer/mercenary for the Life Foundation, an organization that was preparing for the M.A.D. (Mutually Assured Destruction) fallout of the Cold War and sought to provide a comfortable life for their wealthy clients after the impending nuclear holocaust. Carl was one of the organization's security force members who was chosen to be made into one of the superhuman police force members for the utopian future that the Life Foundation sought to bring about. This was done by forcibly extracting multiple offspring from the alien creature known as Venom, after which the offspring were artificially aged to maturity. Carl was bonded with one of these symbiote offspring and became one of the Life Foundation's Guardians.
Carl Mach was created by David Michelinie, Ron Lim, Sam DeLarosa and Al Milgrom, and he first appeared in 1993's Venom: Lethal Protector #4.
The symbiote that Carl was bonded with became known as "Phage," a name largely derived from a Venom toy line that released around the same time. Like Riot however, Carl Mach was never officially known as Phage as this was actually the name of a different symbiote-like character. Carl Mach being named Phage was therefore largely fan-based, but in 2012's Carnage U.S.A. however, Carl's symbiote was officially identified as Phage for the first time. So in the end, the name "Phage" stuck.
Major Story Arcs
During Venom's time as Lethal Protector of San Francisco, Carl and his "siblings" were defeated by Venom and Spider-Man. Trevor's symbiote was artificially aged to dust and his body was caught in a massive explosion.
It was later revealed that the symbiotes had survived due to efforts by the Life Foundation. They broke Eddie Brock out of prison and kidnapped him in a last ditch effort to communicate with their alien "others." Unfortunately Eddie refused to aid them, due to Carnage's example that his "children" became psychopathic killers. After Leslie was killed, supposedly by Brock, Carl went on a rampage to avenge her by killing Brock. Scream covertly killed Carl with a sonic knife however, having snapped from her schizophrenia and her symbiote's influence, believing that the symbiotes and any who host them were evil. Carl's death assisted Donna in misleading the others into thinking Eddie Brock was picking them off. She went on to kill the rest of the symbiote hosts even after her ruse was revealed.
Carl's symbiote survived, and was imprisoned/experimented upon in the Vault along with its siblings (except Carnage and Scream). The symbiotes eventually merged together, and bonded with a man known as Scott Washington to form Hybrid.
In Carnage: USA, the Hybrid symbiote was revealed to have been forcibly separated behind the scenes. The Phage symbiote, along with its siblings, were rendered catatonic as a result of the trauma of the separation. Covert Government Mercury Team, trained with them to teach them specialized tasks. Phage was teamed up with Lieutenant Rico Axelson, Navy Seal Sniper.
Deadpool vs. Carnage
In Deadpool vs. Carnage, Deadpool stole the symbiotes from a government facility to help him combat Carnage. After defeating Carnage he puts the symbiotes on a dog and instructs it to take them back to the government.