The evil Sister Theresa
Sister Theresa (Ornella Muti) is the main villainess from "True Believer," episode 3.10 of The Hitchhiker (airdate March 11, 1986).
Sister Theresa was introduced as a nun serving as a novice in a convent, where she encountered detective Frank Sheen regarding the suicide of a priest. Regarding the claims of demonic activity, Sister Theresa stated that she didn't know about a demon, but warned Sheen to watch out for one. Sheen is later informed by Father Dowling that there was no nun, and the convent had been closed since 1910.
As for Sister Theresa, she was revealed as a demon who had been haunting the abandoned convent since her suicide that same year, and she used her demonic powers to cause the priest's suicide. In the episode's climax, the evil Sister Theresa targeted Sheen by taking the form of his ex-wife, Linda, causing Sheen to embrace her romantically. After Sheen professed his love for Linda, he was shocked to see her turn around and take the form or Terri, Sheen and Linda's deceased daughter. The villainess used her power to create the illusion that the building was shaking, after which Sheen shot Dowling in a state of panic. As a result of Sister Theresa's evil actions, the episode ended with Sheen in a catatonic state with his gun in his mouth, repeatedly pulling the trigger of the unloaded weapon.