This actor appears for about 30 seconds in SODOM & GOMORRAH. The camera stays on him and yet he's not credited.
In THE GIANTS OF THESSALY, this actor, who's seen throughout the film and even has pivotal scenes with dialogue, is not identified. His name in the film is Leocrates. It probably was his first and last film. THE GIANTS OF THESSALY literarily has a boat-load of unknown actors.
This actor appears during the climax in REVOLT OF THE SLAVES. He doesn't have any dialogue but his role is pivotal to the storyline and yet I have no idea who he is.
Probably as bad a case as Mabuna in LAND OF THE PHARAOHS, the identity of the actor standing next to Guy Rolfe in REVAK THE REBEL is not known even if he has a semi-major role in the film. It's a frustrating thing to see an actor on screen who's career is invisible.
Facebook friend Steven Smith wondered about this actor's identity who appears in SLAVE OF ROME. He has lines and his scene is one of the film's highlight but his identity is unknown. To make things worse, the film has a dozen actors with just this film under their belt. And that terrible wig and makeup don't help much. So it's impossible to know who he is unless one talks to someone who worked on the film.