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).

The Public Enemy is a 1931 American pre-Code gangster film produced and distributed by Warner Bros. The film was directed by William A. Wellman and stars James Cagney, Jean Harlow, Edward Woods, Donald Cook and Joan Blondell. The film relates the story of a young man's rise in the criminal underworld in Prohibition-era urban America. The supporting players include Beryl Mercer, Murray Kinnell, and Mae Clarke. The screenplay is based on an unpublished novel—Beer and Blood by two former newspapermen, John Bright and Kubec Glasmon—who had witnessed some of Al Capone's murderous gang rivalries in Chicago.