In the Gun of" this man.  
Lesser known portrayals of this character include John Ireland playing him opposite Tom Tyler and Reed Hadley in a 1949 Samuel Fuller film.  John Carradine played him in a 1940 film also starring Gene Tierney and Henry Fonda which was directed by Fritz Lang.  A song with this man in the title begins with the lyrics "Like a corn in a field I cut you down."  That song was released as a single paired with "Grow Some Funk of Your Own," and is an Elton John song titled "I Feel like a Bullet In the Gun of" this man.  In a recent movie, his brother is played by Sam Rockwell, and his portrayal earned an Oscar nomination for Casey Affleck.  FTP, name this "coward" in a 2007 film about his assassination of Jesse James.
Lesser known portrayals of this character include John Ireland playing him opposite Tom Tyler and Reed Hadley in a 1949 Samuel Fuller film.  
Robert (or Bob) {Ford}