Ty Farell (Daniel Riordan) played the hero Captain Zoom in a cheesy 1950s scifi serial, now the people of planet Pangea recruit him as their real-life hero in the fight against the evil Lord Vox of Vestron (Ron Perlman). Also with Nichelle Nichols, Liz Vassey & Gia Carides.
https://en.wikipedia.org/wiki/The_Adventures_of_Captain_Zoom_in_Outer_Space
Via https://retro.social/@ajroach42/117448110684741838
EDIT: corrected 1940s to 1950s
That’s roughly the plot of Galaxy Quest, right?
And The Three Amigos, too