According to the Ghostbusters, Zuul was a demigod worshipped by the Hittites, Mesopotamians and the Sumerians. Zuul was the minion of Gozer.
At first Zuul posessed a statue on the roof of a building, and later it posessed the body of Sigourney Weaver, which was a much better choice.
"There is no Dana, there is only Zuul."