The Sandman is an antagonist from The Real Ghostbusters cartoon series. He was rather unique in the fact, he was not truly malevolent, rather he was misguided and sought to end war and suffering via putting the entire human race into a 500-year-old slumber. The Sandman made his debut in "Mr. Sandman, Dream Me a Dream", where he was on a mission to stop all war by putting all of mankind to sleep for 500 years. He wished to stop all wars and create peaceful world where dreams only exist.
Winston realized that what they saw were a dream and laid a trap for the Sandman at headquarters. Slimer trapped the Sandman which was successful when all his victims were awakened.