Which actress has won the most Oscars in the Best Actress category?

Katharine Hepburn holds the record with four Oscars as Best Actress for 'Glory for a Day' (1933), 'Guess Who's Coming to Dinner' (1967), 'The Lion in Winter' (1968) and 'On Golden Pond' (1981). Meryl Streep, although she has the record for nominations (21), has won 'only' three Oscars: two for Best Actress and one for Best Supporting Actress.