Azazel
From Super-wiki
The term Celine Demon has been coined on the TWOP boards on September 14th, 2005, in a discussion after the airing of the 1.01 Pilot (episode) and means the demon, who killed the Winchester brothers' mother Mary Winchester.
It derived from a misreading of the words Ceiling Demon] as Celine Dion (Canadian popsinger) by TWOP-user thinkcwik. The singer's name and the nickname for the demon were meshed and the new term stuck.