Otis Miller was a legendary gunslinger often associated with the Wild West. He was the leader of a gang of outlaws called the Otis Miller Boys, who ran from place to place and became the subject of many dime novels. He also had a son at some point named Otis Miller Jr. who became an outlaw.
His revolver can be found in New Austin after the epilogue. However, Arthur can get the revolver through a glitch or an exploit.
Three of the penny dreadful novels that Arthur can get for Jack involve Miller.
A number of details in the game indicate that Miller is based quite directly on Jesse James. In camp, members of the Van der Linde gang can sing an “Otis Miller” song, much of which is identical melodically and lyrically to the actual nineteenth century folksong “Jesse James.” The songs portray Miller and James respectively as good-natured, Robin Hood-like outlaws who were ultimately killed by cowards.
Another campfire song in the game, “Jack Hall,” is based on the outlaw experiences of members of the Younger brothers. Its lyrics describe the “Hall” (Younger) brothers' meeting and uniting with the “Miller” brothers (Frank and Jesse James) before they all embark on the ill-fated Northfield Bank robbery.
Like Miller, the real Jesse James had a son who reputedly became an outlaw for a time. The son, Jesse E. James, was arrested for train robbery in 1898 but was acquitted the following year.