Kerko was originally from Rigel 77, from which he escaped with his little brother. He arrived in Splott, where he obtained two pitbullfrogs and started causing trouble. Jack Harkness tried to capture them, but Kerko's brother was accidentally killed. This left Kerko with a grudge against Jack. Jack tried to interrogate him about the recent surge of Rift activity, but Kerko was unwilling to cooperate and tried to kill Jack.