Final answer:
Jayne Mansfield was the first woman to appear topless in a major Hollywood film, 'Promises! Promises!' in 1963.
Step-by-step explanation:
The first woman to appear topless in a major Hollywood film was Jayne Mansfield in the 1963 film 'Promises! Promises!'. In a scene where she takes a shower, Mansfield's breasts are briefly visible. This caused a stir at the time and marked a shift in Hollywood's approach to nudity in films.