Gwen Cooper was a Cardiff Police Constable when she stumbled across a secret Torchwood 3 operation which involved the death of several people. She joined Torchwood at the invitation of Captain Jack Harkness, who valued her empathic nature and ability to see beyond the facts.
As a Torchwood operative she provided an essential foil to Captain Jack, although her personal agendas often interfered with her duties. Her actions and descisions are often guided by her desire to protect her live-in boyfriend, Rhys. She had a brief, disruptive affair with another operative, Owen Harper.