The shocking ending of the original adaptation of Planet of the Apes was one of the most memorable cinematic finales of all time, but the 1968 classic also left viewers with many questions. Based on the novel by Pierre Boulle, the story envisioned a planet where apes became the dominant species and humans were subjugated as animals. Rife with sly political commentary, the film was also a seminal piece of sci-fi cinema and elevated itself from a campy B-movie to a bona fide box office smash when it grossed $30 million (via Box Office Mojo). Perhaps its most important feat was that it would eventually launch a massive cinematic franchise.
https://screenrant.com/planet-of-the-apes-1968-origina-movie-ending-explained/