De León, who was born Gerardo Ilagan, was a member of the Ilagan clan of Philippine motion pictures, which includes Robert Arevalo, Conrado Conde, Angel Esmeralda, Eddie Ilagan, musical scorer Tito Arévalo, and his daughter Liberty Ilagan. De León was a medical doctor by profession, but his ultimate love for film won him over. He made his acting debut in the 1934 film Ang Dangal. He acted in eight other films before becoming a director. The first film he directed was Bahay-Kubo, starring Fely Vallejo, an actress whom he later married. De Leon produced a number of anti-American propaganda films during World War Two, in collaboration with the occupying Japanese forces and Japanese director Abe Yutaka, who personally chose De Leon for the projects. De Leon was arrested and charged with treason after the Japanese were defeated, and was almost executed by the Filipino government. But at the last minute, he was pardoned when evidence came to light that all during the war, he had secretly assisted the Filipino resistance as well. Nicknamed "Manong", de León is the most awarded film director in the history of the Filipino Academy of Movie Arts and Sciences' FAMAS Awards. From 1952 to 1971, he was awarded seven FAMAS Awards, three of them received consecutively. His 1961 film The Moises Padilla Story was selected as the Philippine entry for the Best Foreign Language Film at the 32nd Academy Awards, but was not accepted as a nominee. All of the films for which he won Best Director also won Best Picture at the FAMAS, namely Sawa sa Lumang Simboryo, Hanggang sa Dulo ng Daigdig, Huwag Mo Akong Limutin, Noli Me Tangere, El Filibusterismo, Daigdig ng Mga Api, and Lilet. One of his unfinished projects was Juan de la Cruz with Fernando Poe Jr.. He is known to fans of cult horror films for the handful of 1960s horror movies he directed, some co-directed with his friend Eddie Romero and co-financed with American money. These films included Terror Is a Man, The Blood Drinkers/ Blood Is the Color of Night, Curse of the Vampires/ Whisper to the Wind, Brides of Blood, and Mad Doctor of Blood Island. Roger Corman hired him in 1971 to direct his gritty Women in Prison filmWomen in Cages, featuring Pam Grier as a sadistic prison warden and Philippines sex symbol Sofia Moran. De Leon died on July 25, 1981 at age 67.
