Tracy the Gorilla (portrayed by Bob Burns) is the Gorilla/ape that is the third member of the group. While he can't speak or write, he is known to draw, and express his feelings through acting.
Zero (voiced by Lou Scheimer) is a mysterious ally who provides the cases for the Ghost Busters. Each case is presented Mission Impossible style in a recorded message that the Ghost Busters pick up at the local drugstore. Zero is not ever seen throughout the fifteen episodes.