You can definitely use the Cisco Kid in your work. O Henry's story (in which Cisco first appeared as a ruthless American outlaw), was published in the U.S. prior to 1923 placing it within the public domain. There are also no character trademark registrations for the Cisco Kid, though the name has been the subject of registrations for candy, fishing lures, and tequila. If you plan to include the Kid's sidekick, Pancho, in your script, beware that his copyright status is not as clear. Pancho did not appear in the O Henry story and was reportedly inspired by Don Quixote's sidekick, Pancho Sanza. His first appearance was in the 1945 film, The Cisco Kid Returns (not to be confused with the 1939 film, Return of the Cisco Kid) and assuming that film was timely renewed, the assignees of Monogram Pictures (Allied Artists International) may own copyright on that character. We say "may" because a number of Monogram films from 1936 to 1946 fell into the public domain. (In other words further copyright research is required.) Our analysis of Pancho is based on the case involving Sherlock Holmes in which it was determined that Sherlock was in the public domain but that the assignees of Arthur Conan Doyle's estate could claim copyright on the characters (for example, Watson's second wife) in stories published after 1922.
