Who Killed Who? is a 1943 Metro-Goldwyn-Mayer film noir animated short directed by Tex Avery. The cartoon is a parody of whodunit stories and employs many clichés of the genre for humor; for example, the score is performed not by the MGM orchestra but by a solo organ, imitating the style of many radio dramas of the era.

Robert O'Connor, also known professionally as Robert Emmett O'Connor and Robert E. O'Connor was an Irish-American actor. He had a lengthy career as a stage actor on Broadway and in vaudeville from 1905-1931; using the stage name Robert O'Connor in both musicals and plays. After transitioning to film, he also used the names Robert Emmett O'Connor or Robert E. O'Connor for his screen credits. He appeared in more than 200 films between 1919 and 1950; specializing in portraying policemen. He is probably best remembered as the warmhearted bootlegger Paddy Ryan in The Public Enemy (1931) and as police Sergeant Henderson pursuing the Marx Brothers in A Night at the Opera (1935). He also appeared as Jonesy in Billy Wilder's 1950 film Sunset Boulevard. He also made an appearance at the very beginning and very end of the Metro-Goldwyn-Mayer cartoon short Who Killed Who? (1943).