The man known as "Junky" Doolb ("Blood" spelt backwards) was an underworld figure with light eyes and light, wavy hair. Doolb shot Fred Mason because Mason had not delivered rigged gambling equipment to his gang as promised. Although he left a false clue implicating Rudy Seton as the killer of Mason, Dick Tracy realized that "J.D" (Junky Doolb) was the real killer. With the help of Mary X, Tracy captured Doolb in Rudy Seton's nightclub.