It is unclear why this term came to be used as a job title on film sets. According to the OED, "It has been suggested that it originated as a term for a master's most able apprentice, or alternatively that it was transferred from earlier use for a member of a ship's crew, but confirmatory evidence for either of these theories appears to be lacking." The earliest known appearance of the phrase in print is 1931 from the "Albuquerque Journal": "Among the electricians .. the department head is the gaffer, his first assistant is the best boy."