I think I know his name now because I found him in some fotoromanzi.
First I found him in Le avventure di Jacques Douglas N. 26: "Poker di spie" (from November 1967). He plays the 'grande capo' of an evil organization called SEVEN (very similar to SPECTRE in the James Bond movies). A nice little role but, unfortunately, he was uncredited:
But what is more interesting is that I also found him in Il re dell'F.B.I. N. 10: "Prima che lei mi uccida" (from December 1968), where he plays a captain:
And in this fotoromanzo there was a good cast list:
It credits a certain Franz Colangeli as 'Il Capitano'. I can't understand who else this character name could refer to so this has to be the name of our unknown friend!