Dr. Samuel "Sam" J. Loomis is a fictional character in the Halloween franchise. A main protagonist of the overall series, Loomis appears on-screen in eight of the thirteen Halloween films, first appearing in John Carpenter's original 1978 film. Donald Pleasence portrayed the character in five films, with Malcolm McDowell taking on the role in the 2007 reimagining and its sequel. In both portrayals, Loomis is introduced as the psychiatrist of series antagonist Michael Myers, driven to pursue and restrain his murderous former patient. He also appears in a flashback in Halloween Kills.

Halloween is a 1978 American independent slasher film directed, co-written, and scored by John Carpenter. Starring Donald Pleasence and Jamie Lee Curtis, with P. J. Soles and Nancy Loomis in supporting roles, the film is set mostly in the fictional town of Haddonfield, Illinois. The plot centers on a mental patient, Michael Myers, who was committed to a sanitarium for murdering his teenage sister on Halloween night when he was a child. Fifteen years later, having escaped and returned to his hometown, he stalks teenage babysitter Laurie Strode and her friends while under pursuit by his psychiatrist Dr. Samuel Loomis.