Trevor was on working as Security Personnel for the Life Foundation when he volunteered to be implated by a symbiote that they extracted fomr Venom and become a member of Life Foundation's Guardian Symbiotes whit four other co-workers from the Security Personel.
Donna another member of Guardian Symbiotes went to test her powers and run into Spider-Man who beat her and when she escaped whit a howercraft. Spider-Man hitched a ride on the underside of the craft whitout anybody noticing. Realising that Spider-Man was inside and coming after Venom, Drake sent all five of his Guardian Symbiotes after him, forcing Spider-Man to team up with Eddie Brock (who had just recently been separated from his Symbiote) to try and defeat these new Symbiotes. Using sonic blasters they managed to hold them off long enough for Eddie to find and re-bond with his Symbiote. Becoming Venom once again.
Venom finally defeated the Guardian Symbiotes by using the same machine that aged the Symbiote 'seeds' ready for bonding and blasting them with it. Causing their Symbiotes to age rapidly and leaving the hosts in a pile of smoke and dust on the floor, but still alive. Drake quickly blew up the research facility and all evidence of what he and the Life Foundation had been up to.
The Guardian Symbiotes survived the destruction of the base. Struggling to control their Symbiotes. They started to search Venom once again to get him to tell them how to control the symbiotes. Donna had some encounters whit Venom before they all decised to go to get the answers they needed. They broked Eddie Brock out of jail (who was whitout his symbiote at the time) and took him to their hideout on the outskirts of Chicago.
They once again asked Eddie for his help with controlling their Symbiotes and once again Eddie refused & instead tried to kill them all even though he was without his Symbiote.
Eddie managed to escape and went on the run but unfortunately for him his disappearance coincided with the murder of Leslie (other female member of the Guardian Symbiotes. This led the others to believe that Brock was the murderer. They no longer wanted his help, they wanted him dead.
The four remaining Guardian Symbiotes tracked Brock down to a warehouse somewhere in Chicago and it wasn't long before another Guardian Symbiotes member was picked off, this time it was Carl, with the same sonic dagger that killed Leslie. The three remaining Guardian Symbiotes captured Brock and tied him up. Not long after we learn that it wasn't Brock killing the other Guardian Symbiotes, it was in fact Donna. Then she killed the last two of the Guardian Symbiotes Trevor and Ramon. Before she killed them she confessed that she could here the 'voices' long before she'd bonded with her Symbiotic other. Donna attacked Eddie who got his symbiote back and won the fight. Donna was then captured and taken away by the same people who had captured Brock earlier.
Even if the host of the symbiote was dead the symbiote wasnt. It and all the other symbiotes whos host was killed fused together. That fused symbiote was also captured and shipped to Vaults research lab. They escaped from there when a guard named Scott Washington freed them. Later the symbiotes bonded whit him and the Hybrid was born.