The movie's publicity still with Paul Newman and Lee Marvin was photographed by British photographer Terry O'Neill and also appears on the jacket of O'Neill's 2003 compilation coffee-table book "Celebrity." In the book, O'Neill recounts how when he arrived on the set to shoot his publicity stills, Lee Marvin was hungover and in a foul mood. Most of the production personnel were steering clear of him. When O'Neill gingerly approached Marvin and introduced himself, Marvin asked, "Are you English?" What O'Neill didn't know at the time was that Marvin was a lifelong Anglophile--he LOVED the British. After that brief encounter, Marvin's mood changed and, according to O'Neill, he couldn't have been more cooperative for the rest of his assignment.
One of Paul Newman's demands was that he got to spend an hour each morning on location in a sauna. That's why his character in the film uses the shower steam to create a sauna early in the story.
Based on a novel called "Jim Kane," that was the working title of the film. The title was changed to take the emphasis off of one character and to stress the partnership of Paul Newman and Lee Marvin.
Newman, Wayne Rogers, and Strother Martin were cast five years earlier in La leyenda del indomable (1967) but not all together. In the parking garage and hotel scenes here, they're actually all together in the same shots.
Jim's white pickup truck is a 1956 Chevrolet Cameo Carrier. One of the earliest "sport" pickups, and the forerunner of the El Camino, examples in excellent condition have sold for well over $50,000 in 2021.