I was about to bring up Victor Frankl. I'm happy you beat me to it. In addition, consider the story of Admiral James Stockdale, who was kept in a P.O.W camp in

I was about to bring up Victor Frankl. I'm happy you beat me to it. In addition, consider the story of Admiral James Stockdale, who was kept in a P.O.W camp in Vietnam for 7 years. His memoir explicitly mentions Stoic philosophy as having been key to his ability to endure.