Brett Halsey didn't believe in this movie and opted to use a the pseudonym Montgomery Ford so people wouldn't associate him with it. The film ended up being his most successful ever and to this day he's credited as Montgomery Ford in Italy.
Tatsuya Nakadai only spoke Japanese, so director Tonino Cervi had to communicate via an interpretor and sign language. Nakadai hadn't ridden a horse before and fell off, fortunately not injuring himself. Brett Halsey said he found Wayde Preston hard to talk to on the set, and most of the time William Berger was high on marijuana. In between takes Halsey once found him stoned in the woodland scene, sitting against a tree, trying to read a newspaper upside down.
The cast is made up of "B" list actors. The one exception is playing the villain Elfago, the very highly regarded Japanese actor Tatsuya Nakadai.
Bud Spencer was usually bearded in his Western roles, but the one you see in TODAY WE KILL... is a false one. This was because Bud had just finished filming another Western called BEYOND THE LAW, in which he played an uncharacteristic role as a clean-shaven, suit-wearing, miner's boss (starring Lee Van Cleef), and did not have time to grow a full beard for the Irish outlaw, O'Bannion, in Tonino Cervi's film.