“The Phantom Empire” (1935-Mascot serial).
The villains were part of an underground city. Ruled by blonde Dorothy Christie. Lots o’ robots.
Thanks, that made me remember.
I remember when I was around 6 or 7 around 1953, my Brothers would take me to the “Bay Theater” on Saturdays. There was always a Roy Rogers, Gen Autry, or Tarzan movie on. First thing was a serial. My favorite one was “Rocket Man” each episode always ended with a cliff hanger. In fact sometimes it actually was one of him being thrown off a cliff.
In the next episode he starts off waking half way down and managing to turn on the control for his rocket pack and escaping.
My least favorite was one of the cavalry chasing a gang of what must have been outlaws or the outlaws chasing the cavalry.