Trevor Cole 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. Trevor was picked from the organization's security force made up of cops, soldiers, and mercenaries to take part in an experiment. The alien creature known as Venom went through a procedure where multiple "offspring" were forcibly extracted from it and then artificially aged to maturity. Trevor was paired up with one of these symbiotes, and he and his fellow Guardians were intended to serve as the superhuman police force for the utopian future the Life Foundation sought to bring about.
Riot was created by David Michelinie, Ron Lim, Sam DeLarosa and Al Milgrom in 1993 and first appeared in Venom: Lethal Protector #4.
Trevor Cole was often identified as Riot, but this name comes from the Venom action figure line. A mere glance at the Riot action figure - or reading the backstory of the action figure on the card ("a sewer-dwelling mutant bonded with a symbiote during the invasion") - leaves many questions as to how this association first occurred. The made-for-toys character of Riot is not Trevor Cole, and bares zero resemblance to him, so Trevor being known as Riot began unofficially on the internet. In 2012's Carnage U.S.A. however, Trevor's symbiote was officially identified by the name of Riot for the first time. Despite it never truly having been his, it seems that the name "Riot" has stuck.
Major Story Arcs
During Venom's time as Lethal Protector of San Francisco, Trevor 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. Scream killed Carl with a sonic knife after killing Leslie, 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. When her ruse was revealed she stabbed Trevor in the chest and killed him.
Trevor'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 Riot 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. Riot was teamed up with Petty Officer Howard Ogden, of Marine Corps Forces Special Operations Command (MARSOC) Reconnaissance.
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.