His films as director include the "Animal Trilogy", consisting of "The Bird with the Crystal Plumage" (1970), "The Cat o' Nine Tails" (1971) and "Four Flies on Grey Velvet" (1971); the "Three Mothers" trilogy, consisting of "Suspiria" (1977), "Inferno" (1980) and "The Mother of Tears" (2007); and the standalone films "Deep Red" (1975), "Tenebrae" (1982), "Phenomena" (1985), and "Opera" (1987). He co-wrote the screenplay for Sergio Leone's "Once Upon a Time in the West" (1968) and served as George A. Romero's script consultant on "Dawn of the Dead" (1978), of which he also composed the soundtrack with his long-time collaborators Goblin.