Cathulhu

Cathulhu is a villain that appears in the Ghostbusters cartoon, specifically the episode entitled "The Collect Card Of Cathulhu" - he is a homage to Cthulhu but had the name purposely misspelled due to copyright issues: also many of the Lovecraftian themes were toned down to keep in with both the more comedic Ghostbusters world and the family-friendly image of the cartoon.

History
Cathulhu is a demonic Old One, a being beyond classification and who - in Egon's words - made Gozer look like "little Mary sunshine" - he is too powerful to be scanned and as such is arguably the most powerful supernatural entity the Ghostbusters have ever faced, his only weakness seemed to be powerful magic and the Ghostbusters also found a way to harm him via using their particle streams to ionize a roller coaster track, causing lighting to strike it, effectively sending 100 giga volts of electricity though it, yet even this didn't kill Cathulhu - it simply put him back into his slumber.

Cathulhu was served by a human cult that sought to bring him out of slumber and end the world (and almost succeeded) as well as demonic minions known as "Spawn Of Cathulhu" - like their master these elements are very Lovecraftian - another striking homage to Lovecraft was the means by which the cult ultimately summoned Cathulu, the evil book known as the Necronomicon.