Arthur R. Barker (June 4, 1899 – January 13, 1939) was an American criminal, the son of Ma Barker and a member of the Barker-Karpis gang, founded by his brother Fred Barker and Alvin Karpis. Generally known as "Doc", Barker was typically called on for violent action, while Fred and Karpis planned the gang's crimes. He was arrested and convicted of kidnapping in 1935. Sent to Alcatraz Federal Penitentiary in 1936, he was killed three years later while attempting to escape from the Rock.
Barker is described by one writer as "a dimwit and a drunk", who was little more than a brutal thug. However, fellow Alcatraz inmate Henri Young said of him that he was "determined and ruthless, and that once he started on anything nothing could stop him but death."