Much of the original Planet of the Apes was a grueling desert film shoot, with actors wearing prosthetic make-up that was cutting-edge for 1968 but was still incredibly cumbersome. Their greatest champion, remembers the one and only Dr. Zaius, was star Charlton Heston—who apparently insisted everyone call him “Chuck.”
Source: io9 – Dr. Zaius Fondly Remembers Working With ‘Chuck’ Heston on Planet of the Apes