One of the clockwork-like-phenoms of Hollywood is that there are invariably at least two projects with the same theme, or story line, chugging through the development pipeline at any given point. "Tombstone" vs. "Wyatt Earp" is a good example. In 1967-68, two films about the Wild Bunch were perking. The one with the biggest profile was William Goldman's "Butch Cassidy & The Sundance Kid" which Twentieth Century Fox was producing to great buzz. Warner Brothers had a competing film, "The Wild Bunch" and intended to get it in theaters before Butch & Sundance.
Allegedly, the guy who thought up the basic story of WB was Roy Sickner, the original Marlboro Man. Then, of course, Sam Peckinpah got on board and everything changed. Believe it or not, Sam actually thought if you showed violence the way it really is, people would shun violence. The "bullet driven ballet" is a long way from the Goldman version and has very little to do with the historical Wild Bunch, but both films deal with the theme of changing times vs. the men who could not.
The Wild Bunch Walkdown
"It ain't like it used to be, but It'll do."
—Freddie Sykes (Edmond O'Brien) to Pike