1. The original movie was written by Rod Serling, creator of The Twilight Zone
Planet of the Apes was based on the French novel La Planète des singes by Pierre Boulle, the rights to which were bought by Arthur P. Jacobs before the book was even published. Jacobs then brought on The Twilight Zone creator and lead writer Rod Serling to pen the script.
Serling’s biggest contribution to the adaptation was the now iconic ending where Taylor comes across the Statue of Liberty to realise he’s been on Earth all along (spoilers). According to reports and rumours, Boulle was unhappy with this change but eventually came round to the idea.
In an interesting connection to The Twilight Zone, the idea of someone’s sleep chamber being broken and dying while in hibernation, was used in the Season Two episode The Rip Van Winkle Caper.
Planet of the Apes often feels like a Twilight Zone movie with its social commentary masked by a science fiction veil (something the show thrived on) and its twist ending. Someone even re-edited the movie to look like a Twilight Zone episode, including Rod Serling narration!