Planet of the Apes (1968)

Complex sociological themes run through this science-fiction classic about three astronauts marooned on a futuristic planet where apes rule and humans are slaves. The stunned trio discovers that these highly intellectual simians can both walk upright and talk. They have even established a class system and a political structure. The astronauts suddenly find themselves part of a devalued species, trapped and imprisoned by the apes.