Toxin is the name given to Patrick Mulligan and his symbiotic alien partner. He is the third of the Marvel Universe's growing collection of symbiotic characters, and presents himself as the first true Symbiote hero—despite occasionally allying himself with his "grandfather" Venom.
Toxin's father is Carnage, another symbiotic entity. Cletus Kasady (Carnage's human half), became disturbed upon discovering he was pregnant in the first place (being male), and intended to kill it upon "giving birth."
Carnage planted the alien symbiote onto Patrick Mulligan with the intent on killing the duo later. This plan however was foiled by none other than Venom, who fought off Carnage and in fact gave the very young symbiote its name: Toxin, after itself.