Lee Van Cleef was very grateful for his part in this movie, as he had fallen on hard times due to his heavy drinking. This movie effectively marked a resurgence in his career. Van Cleef had taken up painting in the interim as a way of making money.
"Monco" is officially not the same character as "Joe" in A Fistful of Dollars (1964). This was the finding of an Italian court that adjudicated the lawsuit brought by Jolly Films, producer of A Fistful of Dollars. After the release of that movie, writer and director Sergio Leone had a falling out with the producers and made this movie with a different producer, Alberto Grimaldi. Jolly Films sued, claiming ownership of the "Joe" character, but lost when the court decided that the western gunfighter's persona, characterized by the costume and mannerisms, belonged to the public domain's folklore.
The town of El Paso, designed by Carlo Simi in Almería, Spain, was the biggest set for which writer and director Sergio Leone was responsible at the time. It was reused for several scenes in The Good, the Bad and the Ugly (1966), in which it stood as several different towns. It's still standing to this day and is called "Mini Hollywood."
Gian Maria Volontè performed his lines in English, although he needed a translator to tell him everything word-for-word, as he did not speak the language. Contrary to some sources, his voice is not heard in the English version, in which his lines are dubbed by veteran voice actor Bernie Grant, who also voiced Volontè in A Fistful of Dollars (1964) and the Embassy Pictures version of Quién sabe? (1967).
The Man with No Name (Clint Eastwood) calls himself Monco in this movie. "Manco" is Spanish for "lame of one hand", "one handed", or "one armed", which is pretty appropriate considering his habit of fighting, drinking, et cetera with his left hand only. His right hand always remains on his gun underneath his trademark poncho.
Sergio Leone: [theme] Monco (Clint Eastwood), Colonel Douglas Mortimer (Lee Van Cleef), and El Indio (Gian Maria Volontè).