Complex sentence: The top stars of their respective sexes, Humphrey Bogart and Katharine Hepburn, both starred in the classic adventure film "The African Queen", for which Bogart won his only Oscar.
Split into simpler sentences: The top stars of their respective sexes are Humphrey Bogart and Katharine Hepburn. They starred together in the classic adventure film "The African Queen", for which Bogart won his only Oscar.