During production of this movie, Charles Bronson said: "It's not the role I accept, it's the possibility of the picture being entertaining. I work for the whole, not for myself. I work for the audience. I've always felt that people deserve that much when they pay to see your picture. This is why, when I choose a role, I believe in giving what I feel is worth the price of a ticket. I believe in giving service."
Charles Bronson had it stipulated in his contract that he would only spend eight hours a day working throughout the shooting of this picture. This included time spent having his makeup done at the start of the day.
Once asked about comparisons to his character in this movie with Humphrey Bogart's in Casablanca (1942), Charles Bronson replied: "I play Charles Bronson".
While filming, Fernando Rey was much more of an a celebrity for the locals than Charles Bronson. This was due to the fact that he had appeared in so many Spanish language movies over the years.