Frederick George Barker was an American criminal who, along with Alvin Karpis, co-founded the Barker-Karpis gang, which committed numerous robberies, murders and kidnappings during the 1930s. Barker was the youngest son of Ma Barker, all of whose children were criminals. He was killed in a lengthy gunfight with the Federal Bureau of Investigation (FBI) in 1935.

Alvin Francis Karpis, was a Canadian–American criminal of Lithuanian descent known for being a leader of the Barker–Karpis gang in the 1930s. Nicknamed "Creepy" for his sinister smile and called "Ray" by his gang members, Karpis led the gang along with Fred Barker and Arthur "Doc" Barker. There were only four "public enemies" ever given the title of "Public Enemy #1" by the FBI and he was the only one to be taken alive. The other three, John Dillinger, Pretty Boy Floyd, and Baby Face Nelson, were all killed before being captured. He also spent the longest time as a federal prisoner at Alcatraz Federal Penitentiary, serving twenty-six years.