Abaddon was a gigantic life-draining demon and the son of The Beast from Doctor Who - he acted as an antagonist in Torchwood (itself a spin-off of the more famous Doctor Who universe): mainly in the "End Of Days" storyarc.
Abaddon was an ally of the Light, a group of powerful energy-beings who fought against Pwccm and the Dark, an opposing faction of energy-beings. They fought together for centuries, travelling the dimensions until they were caught up in the Cardiff rift.
A 1827, archaeological expedition excavating the ruins of Babylon found a stone tablet depicting a Demon standing above a city.
In 1876, the Rift was opened in Tretarri, where Abaddon and Pwccm fought. Though Abaddon appeared to be defeated, he had in reality faked the loss so that he could gain power. He also set his servant, Bilis Manger, to have the event recorded in a special diary, which would be used later to free him.
Later, Bilis set in motion a series of events designed to manipulate the Torchwood 3 team into using the Rift manipulator to open the rift and release Abaddon. Only Jack Harkness stood in his way. He was eventually killed by Abaddon, the Demon dying in the process due to the excess life (Jack is an immortal, thus the strain it took to "kill" him caused Abaddon to perish).
Following the defeat of Abaddon, the Light was greatly weakened and was forced to fight against the Dark and Pwccm on their own. After Torchwood sealed the Dark away and sent the Light back into the Rift to protect it, Abaddon's ashes appeared out of the ground and were recovered by Bilis Manger to be buried outside of Britain.
- Abbadon was known of by the Xylok Mr Smith in The Sarah Jane Adventures.