Ratsasan (transl. Demon; pronounced [ராட்சசன்]) is a 2018 Indian Tamil-language slasher psychological horror-thriller film directed by Ram Kumar, of Mundasupatti (2014) fame. The film stars Vishnu Vishal, Amala Paul, and Saravanan while Kaali Venkat, Vinodhini Vaidyanathan, and Ramdoss play supporting roles. The film features music and background score composed by Ghibran, cinematography by P. V. Shankar and editing by San Lokesh. The film tells the story of an aspiring film director who becomes a police officer after his father's death and tries to track down a serial killer.

The film was released on 5 October 2018 to generally positive critical reviews. It was remade in Telugu as Rakshasudu and in Hindi as Cuttputlli (see below).