Pwccm was a demon allied with the sentient particles known as the Dark, of the same race as Abaddon. He was an enemy of both Abaddon and the Light. He looked like Abaddon but his skin was royal blue.
Pwccm was beneath in Cardiff for countless ages, emerging to wage war on Abaddon either to take control of the Rift or to escape it. Like Abaddon, he allied himself with a group particles of living light native to the Rift, the Dark, and acquired a human follower, Cafard Manger.
In 1876 their battle erupted onto Bute Terrace. Abaddon faked his defeat and Bilis Manger, foreseeing the Dark's triumph, set in motion a series of events to protect the Light until the moment came for them to act.
With the death of Abaddon, Pwccm and his allies were able to imprison most of the Light. He sent the Dark to openly combat the Light in Cardiff. However, Bilis Manger and Torchwood 3 were able to successfully imprison the Dark in a wooden box and send the Light down to imprison Pwccm. (PROSE: The Twilight Streets)