Nanook of the North
1922Building the igloo
Widely credited as the first commercially successful feature-length documentary, though 'documentary' undersells how staged it was: the man billed as Nanook was really Allakariallak, some of the hunting techniques shown had already been abandoned in favor of rifles, and Flaherty had his cast re-enact a version of traditional life for the camera. It's still one of the founding arguments in an argument documentary filmmaking has never fully settled -- how much reconstruction a 'true' record can contain.