Alien father (Virus)
After his mating partner and child fell through the Rift, an alien father he set about trying to find them. (PROSE: Virus)
He travelled to Cardiff in 2009, discovering that his partner had died in the Rift. Before he could reach his surviving son, interreference by Torchwood Three caused the baby to unlatch from its host, causing the host to kill the baby and herself. (PROSE: The Wrong Hands)
The father then set out for revenge. He acquired some doses of the Kagawa Virus from a black market trader, and broke into the Torchwood Hub using a camouflage suit. Once inside, he infected Jack Harkness and Gwen Cooper with the virus. The alien father was then killed when Ianto Jones shot him in the head with a shotgun. (PROSE: Virus)