Kerko

Kerko was a Blowfish criminal who came to 21st century Cardiff via the Cardiff Rift.

Biography
Kerko was originally from Rigel 77, which he was able to escape from with his little brother. He arrived in Splott, where he was able to obtain two pitbullfrogs and started causing trouble. Jack Harkness tried to capture them, but during the course of the capture 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 eventually tried to kill Jack.

When the Undertaker's Gift was activated, the Torchwood Hub started to break down, allowing Kerko to escape. When Jack Harkness returned to the Hub, Kerko tried to kill him in revenge. With the help of a young Vortex Dweller, Jack was able to kill Kerko by electrocuting him. After the Vortex Dweller repaired the damage to time, Kerko was brought back to life and returned to his proper place. (TWN: The Undertaker's Gift)