Final theatrical feature film writing collaboration of long-time co-writers I.A.L. Diamond and writer-director Billy Wilder.
After his miserable experience on Fedora (1978), writer-director Billy Wilder had retired from films. However, he agreed to make this film once Jack Lemmon and Walter Matthau had signed on.
When director Billy Wilder was hired by MGM to do an American version of the French comedy Il rompiballe (1973), he said, "I hadn't been working enough, and I was anxious to get back on the horse and do what I do--write, direct. This wasn't a picture I would have chosen."
Some reports state that Klaus Kinski turned down 'Raiders of the Lost Ark' (1981) to make this movie simply because the producers were offering more money. It was actually the starring role in the same year's horror movie 'Venom' (1981), and not a supporting role in 'Buddy Buddy' (1981), that actor Klaus Kinski preferred over 'Raiders of the Lost Ark' (1981). Kinski wanted a starring role over a supporting one. He did this 'Buddy Buddy' (1981) after 'Venom' (1981).
Two weeks into principal photography, co-writer/director Billy Wilder felt he had miscast the hit-man character with Walter Matthau, that the picture did not work with two comic leads, the Matthau part needed to be in a serious mold, like with a Clint Eastwood.