The character of US Marshal Heck Short (Russ Conway) was based on two actual lawmen that were key players in the story of the Dalton Gang - US Deputy Marshals Ed Short and Heck Thomas. One member of the Dalton Gang - "Blackfaced" Charley Bryant - was captured by Deputy US Marshal Ed Short. When Bryant grabbed a gun from a railroad worker assisting Short, both Bryant and Short were killed in the subsequent gunfight. Deputy US Marshal Heck Thomas pursued the Daltons relentlessly, and according to Emmett Dalton the pressure put upon the gang by Thomas was a prime factor in their decision to attempt to rob two banks simultaneously in Coffeyville, Kansas. The robbery was a failure when the gang was recognized, and most of the gang was killed in the ensuing gun battle, with the exception of Emmett Dalton who received 23 gunshot wounds but survived.
When Cheyenne and Doc Johnson arrive by stagecoach, the voice of the driver is dubbed by William Fawcett who played that type of role in many a western throughout his movie career.
Doc Johnson may have been partly inspired by Dr. Thomas Hodges, AKA Dr. Tom Bell, the "Outlaw Doc", who was said to be one of the first outlaws to organize a stagecoach robbery. One account of Hodges stated "he was known for his natural leadership abilities, and people were drawn to him."