Slimer

Slimer also known as "The Spud" "Disgusting Green Blob", "Onionhead", and "Little Spud", was a minor villain from the original Ghostbusters film, ironically this is his only real moment of being a villain as he was protrayed as a hero in the sequel and cartoon series - yet in an odd turn of events Slimer would again become antagonistic in the Ghostbusters videogame.

More of a nuisance than threat Slimer is infamous for being the ghost who "slimed" Peter Venkman and was originally more frightening in appearance and mannerism - being softened down once he was established as a hero/mascot for the series.

On a side-note Slimer also became an antagonist in one of the Ghostbusters cartoon episodes where, due to one an experiment gone wrong, he produced hundreds of tiny Slimer clones and ultimately grew into a gigantic version of himself once the group tried to fix the problem (becoming a parody of King Kong).

Slimer is also somewhat famous for being the first ghost that the Ghostbusters successfully captured and thus helping to establish the organization as the soon-to-be-famous ghost-capturing crew.