)[1] The son of Luigi and Luisa Castellano,[2] Oswaldo was born in Agrigento, Sicily, and moved with his family to the United States when he was two years of age.

Joe (1945), The Clock (1945), The Postman Always Rings Twice (1946), Guilty (1947), Loves of Carmen (1948), Saigon (1948), Sands of Iwo Jima (1949), White Heat (1949),Quicksand (1950), Highway 301 (1950), City That Never Sleeps (1953), Island in the Sky (1953), Law and Order (1953), Princess of the Nile (1954), Until They Sail (1957), and I, Madman (1989).

Cassell was later cast in two syndicated programs starring Jim Davis: Stories of the Century, in the role of gunman Luke Short, and Rescue 8, as Johnny French in "One More Step."

Cassell also guest-starred in several television series, including The Loretta Young Show (1955), as "Oley" in James Arness's TV Western series Gunsmoke in the 1956 episode "Hack Prine" (S1E26), the 1959 premiere episode of The Untouchables ("The Empty Chair"), Rawhide (1960), and The Beverly Hillbillies (1963).

At age 13, she had the role of Pony Hutchinson in the Walt Disney Studios film Emil and the Detectives (1964).