An Enterprise astrobiologist who lends her body to Thalassa in Return to Tomorrow.
Lieutenant Commander Ann Mulhall is an astrobiologist aboard the Enterprise. In Return to Tomorrow she is part of the group who meets the ancient beings stored beneath the surface of a dead planet, and she agrees to let the consciousness of Thalassa enter her body.
While Thalassa inhabits her, Mulhall's own mind is held in a receptacle, and Thalassa is tempted to keep her body for good. When the beings finally depart, Mulhall is restored to her own body. She was played by Diana Muldaur, who later played Katherine Pulaski.