Doctor Who: The Krotons (1968) written by Robert Holmes and directed by David Maloney
The Second Doctor (Patrick Troughton) lands on the Gonds' planet. They are a simplistic tribe of people who are dominated by the Krotons. Hundreds of years ago, the Krotons landed on the planet and war broke out with the Gonds. With their superior technology, the Krotons won and enslaved the Gonds. Currently, their big demand is the offering of the two most intelligent Gonds to be companions to the Krotons. Those Gonds are never seen again. The Doctor and his companions discover that the Kroton companions are being killed. Things have got to stop and the Doctor is ready to take action.
The story is fairly interesting. The menace is presented early but the whole situation is explained at a slower pace. The show holds off on showing the Krotons, which is good since the outfits are really unimpressive. They look like boxy, shiny robots with leather skirts hiding the actors' legs. Not scary at all. What they use the intelligent people for is interesting if not believable. Troughton is great as always.
Recommended if you can handle the poor visual design of the villains.