Robert Albert Bloch was an American fiction writer, primarily of crime, psychological horror and fantasy, much of which has been dramatized for radio, cinema and television. He also wrote a relatively small amount of science fiction. His writing career lasted 60 years, including more than 30 years in television and film. He began his professional writing career immediately after graduation from high school, aged 17. Best known as the writer of Psycho (1959), the basis for the film of the same name by Alfred Hitchcock, Bloch wrote hundreds of short stories and over 30 novels. He was a protégé of H. P. Lovecraft, who was the first to seriously encourage his talent. However, while he started emulating Lovecraft and his brand of cosmic horror, he later specialized in crime and horror stories working with a more psychological approach.

Bloch was born in Chicago, the son of Raphael "Ray" Bloch (1884–1952), a bank cashier, and his wife Stella Loeb (1880–1944), a social worker, both of German Jewish descent. Bloch's family moved to Maywood, a Chicago suburb, when he was five; he lived there until he was ten. He attended the Methodist Church there, despite his parents' Jewish heritage, and studied at Emerson Grammar School. In 1925, at eight years of age, living in Maywood, he attended (alone at night) a screening of Lon Chaney, Sr.'s film The Phantom of the Opera (1925). The scene of Chaney removing his mask terrified the young Bloch ("it scared the living hell out of me and I ran all the way home to enjoy the first of about two years of recurrent nightmares"). It also sparked his interest in horror. Bloch was a precocious child and found himself in fourth grade when he was eight. He also obtained a pass into the adult section of the public library, where he read omnivorously. Bloch considered himself a budding artist and worked in pencil sketching and watercolours, but myopia in adolescence seemed to effectively bar art as a career. He had passions for German-made lead toy soldiers and for silent cinema.