You gotta love this Amazon description, which assumes that we know who these fellows are:
“FBI agent Brad joins Tony and Nick, the self styled Supermen who battle crime wearing bullet-proof super-suits. They are on a case involving radioactive counterfeit money and people who can be broken down into precious jewels. With some really nice stunts and awesome kung fu, gimmick weapons & gymnastics!”
I mean, I wasn’t interested and then you hit me with gymnastics?
Director Gianfranco Parolini is better known for his Sabata films, as well as God’s Gun. For this movie, he went to Yugoslavia to get the adventures of these three heroes to the big screen. And it wasn’t easy — for one stunt, actor Aldo Canti jumped out of a 20 feet high window, hit a trampoline and then jumped into a truck moving at full speed.
After this movie, the Supermen went around the world: Japan in Three Supermen at Tokyo, Africa in Three Supermen in the Jungle, Hong Kong in the xenophobically titled Supermen Against the Orient, and seemingly have run out of countries, they went back in time to the wild west in The Three Supermen in the West.
Tony is played by Tony Kendall, who is also in The Whip and the Body and The Return of the Blind Dead, as well as the Kommisar X series of films. And Nick, another of the Supermen, was played by actor/stuntman Aldo Canti, a real-life thief with strong mob ties that was released from jail just to appear in this film. He was replaced by Sal Borgese in the other films in this series before coming back for the Turkish co-production Supermenler in 1979.
You can watch this whole thing on YouTube.