The bartender's (Robert Mitchum's brother John) character's name is Elmer. When JP goes to the bar to get Jason, Elmer makes a move for a gun behind the bar. JP shoots the bar, resulting in Elmer getting a fist full of splinters. JP says "I told you Elmer..." At the end when JP runs through the bar, he points the gun at Elmer and says "stay right there, Johnny."
El Dorado is actually part of a remake trilogy by the same director, Howard Hawks. The first was 'Rio Bravo' (1959); 'El Dorado' was next in 1967; and the final variation was 'Rio Lobo' in 1970. El Dorado is the only humorous (and by many critics acclaimed as the best) version of the three.