Robert Arthur Jr. (November 10, 1909 – May 2, 1969) was an American writer and editor of crime fiction and speculative fiction known for his work with The Mysterious Traveler radio series and for writing The Three Investigators, a series of young adult novels.
For his radio work, Arthur—together with writing partner David Kogan—was honored with three Edgar Awards by the Mystery Writers of America. He also adapted at least one story, and had several of his own adapted by others, for Alfred Hitchcock's TV show, Alfred Hitchcock Presents.