Two astronauts land on a planet populated by apes, but these chimps are no chumps and the men find themselves imprisoned and at the mercy of their furry captors. The enigma of the planet's history, juggled through Heston's humiliating experience of being studied as an interesting laboratory specimen by his ape captors, right down to his final startling rediscovery of civilisation, is quite beautifully sustained. One interesting fact is that the aristocratic orangutan Dr. Zaius was originally to be played by legendary actor Edward G. Robinson; test footage even exists of Robinson in the role. He later backed out, announcing that, as a septuagenarian, he was far too old to spend five hours a day in makeup. In 2001, Planet of the Apes was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant".