Robert Jay Arthur, Jr. (November 10, 1909, Corregidor, Philippines, - May 2, 1969, Philadelphia, Pennsylvania) was a mystery writer known for The Mysterious Traveler radio series and his Three Investigators series of novels. He is frequently confused with the film producer Robert Arthur, who was nine days older than mystery writer Robert Arthur, Jr.
Arthur was a graduate of the University of Michigan. Between 1930 and 1940, his stories were published in Amazing Stories, Argosy All-Story Weekly, Black Mask, Collier's, Detective Fiction Weekly, Detective Tales, Double Detective, The Illustrated Detective Magazine, Mystery, The Phantom Detective, The Shadow, Startling Stories, Street & Smith Mystery Reader, Street & Smith's Detective Story Magazine, Thrilling Detective, Unknown Worlds and Wonder Stories. He wrote a number of mystery books for children.
Arthur worked on the anthology television series Alfred Hitchcock Presents. In the 1950s and 1960s, as an uncredited ghost editor, Arthur anonymously compiled more than a dozen anthologies of mystery, suspense and supernatural stories, books purportedly edited by Alfred Hitchcock. They were authorized by Hitchcock but were entirely edited by Arthur, who typically included at least one of his own stories in most of the anthologies. For each book he was the ghostwriter of a foreword allegedly authored by Hitchcock.
Arthur, along with his writing partner David Kogan, was twice honored by the Mystery Writers of America with an Edgar Award for Best Radio Drama: In 1950, for Murder by Experts, and in 1953 for The Mysterious Traveler.
Other radio credits include: Dark Destiny (1942), Adventure Into Fear (1945), The Sealed Book (1945), The Teller of Tales (1950) and Mystery Time (1952).
Robert Arthur, Jr. died in Philadelphia in 1969.