Zuul and Vinz Clortho are the primary servants and harbingers of Gozer The Gozerian. Worshipped as demigods, they are known respectively as The Gatekeeper and The Keymaster. Their goal: possess a mortal male and female, perform a sexual rite combining their powers and open a gateway to allow The Destructor entry into a given world. After opening the portal, they take their places as guardians of Gozer's cosmic pyramid. The Terror Dogs are similar in appearance: horned (the male Vinz Clortho has longer horns) dog-like quadrupeds with powerful, dark-colored bodies, blazing demonic red eyes and vicious fangs and claws.
In Ghostbusters terminology from West End Games' role-playing game, The Terror Dogs would each rank as a Class 7 Metaspectre. In addition to their ability to dematerialize and possess mortals, The Terror Dogs exhibit other supernatural powers such as summoning lesser entities, levitating, telekinesis and shape-changing (usually the physical form of those they possess into their own horrific forms).
Atop 550 Central Park West (55 Central Park West), The Gozerian Temple featured twin gargoyles of The Gatekeeper and Keymaster, within which they manifested and emerged from during a colossal thunderstorm shortly before the "Manhattan Crossrip of 1984." They quickly tracked down and possessed their chosen mortal "fleshbags," specifically Dana Barrett (Sigourney Weaver) and Louis Tully (Rick Moranis). Eventually, Vinz Clortho reunited with Zuul after waiting 8,000 years. The two kissed passionately, then proceeded to the rooftop shrine to worship Gozer, perform the rite and summon their dark master. When Gozer appeared, It proceeded to lovingly pet them, when It was interrupted by the Ghostbusters' arrival. When the Ghostbusters finally resorted to crossing the streams, The Terror Dogs were hurled back along with Gozer to their hellish realm. And there they await for yet another chance to fulfill their unending goal of unleashing The Destructor once more. While not necessarily the origin of the word "Zuul," there is a similarity with the ancient Maya word for dog, "tzul".
Zuul's name was referred by Patty Tolan in the remake of the original film Ghostbusters (2016) after hearing strange recordings, implying that the setting of this film is a parallel universe to the original film and its sequels'.
In the IDW Comics' crossover Ghostbusters 101, Patty's team meets their male counterparts from the original film when their universes collide, resolving the film's cliffhanger.