Jim aka The Waco Kid was played by Gene Wilder. Wilder was not the first actor cast in the role however. Production began with Gig Young as the Waco Kid. On the first day of shooting, the scene where the drunk Waco Kid hangs from a bunk asking if Bart is black, it was obvious that he was actually drunk (he had had an alcohol problem for years) and proceeded to undergo a physical collapse on set. Brooks shut down production for a day.
While working on the Young Frankenstein script, Wilder was offered the part of the Fox in the musical film adaptation of Saint Exupéry’s classic book, The Little Prince. When filming was about to begin in London, Wilder received an urgent call from Mel Brooks, who was filming Blazing Saddles, offering Wilder the role of the “Waco Kid”. Wilder shot his scenes for Blazing Saddles and immediately afterwards filmed The Little Prince. Young later sued Warner Bros. for breach of contract.
Wilder’s sometimes sublime delivery fit perfectly with Blazing’s over the top dialogue, as demonstrated here in this famous line:
Wilder has a very strong connection to Mel Brooks. In 1963, Wilder was cast in a leading role in Mother Courage and Her Children, a production starring Anne Bancroft, who introduced Wilder to her then-boyfriend Mel Brooks. A few months later, Brooks mentioned that he was working on a screenplay called Springtime for Hitler, for which he thought Wilder would be perfect in the role of Leo Bloom. Brooks elicited a promise from Wilder that he would check with him before making any long-term commitments with any on Broadway or off-Broadway productions. Months went by, and Wilder toured the country with different theatre productions, participated in a televised CBS presentation of Death of a Salesman, and was cast for his first role in a film—a minor role in Arthur Penn’s 1967 Bonnie and Clyde. After three years of not hearing from Brooks, Wilder was called for a reading with Zero Mostel, who was to be the star of Springtime for Hitler and had approval of his co-star. Mostel approved, and Wilder was cast for his first leading role in a featured film, 1968′s The Producers.
The Producers eventually became a cult comedy classic, with Mel Brooks winning an Academy Award for Best Original Screenplay and Wilder being nominated for an Academy Award for Best Supporting Actor. Nevertheless, Mel Brooks’ first directorial effort did not do well at the box office and was not well-received by all critics; New York Times critic Renata Adler reviewed the film and described it as “black college humor.”
(partial sources: IMDB & Wikipedia)