Johnny Sheffield's father, Reginald Sheffield, was a talented actor who began his career as a child star and later transitioned to character acting. Sheffield made his Broadway debut at the tender age of seven in the original cast of "On Borrowed Time".
When Maureen O'Sullivan, the actress who played Jane in the Johnny Weissmuller Tarzan series, decided to leave the role, a creative solution was needed. According to the Legion of Decency, since Tarzan and Jane weren't married, they had to adopt a son. Weissmuller himself chose Sheffield to play the role of Boy, a character inspired by Bobby Nelson's portrayal in Tarzan the Mighty (1928).
As an athletic and naturally talented individual, Sheffield was taught to swim by none other than the swimming Olympian Weissmuller. His successful portrayal of Boy in Tarzan Finds a Son! (1939) led to MGM signing him to six more films as Tarzan's Boy.
However, by the time Tarzan and the Mermaids (1948) was released, Sheffield had outgrown the role, and the film simply mentioned that he was away at school. After being dropped by MGM, Monogram Studios picked him up for a series of movies based on the Roy Rockwood Bomba: The Jungle Boy (1949) franchise.
Sheffield went on to make twelve films in this series between 1949 and 1955, solidifying his status as a talented young actor in the world of cinema.
