Below is a very early digital 3D rendered film (possibly the first one, ever). It was created in 1972 by Ed Catmull (the founder of Pixar) and Fred Parke with a little help from Robert B. Ingebretsen.
The best part of this film is not even the 3D rendering itself, but the outtakes and “making of” footage that has been interwoven throughout, including footage of a plaster replica of Ed’s hand onto which he is meticulously mapping the polygon vertices that make up the three dimensional model (around 1:30). That’s really remarkable. The math that we take for granted for rendering 3D was being invented, real time, to create this video. (Ed’s credited for having working out that math to handle things like texture mapping, 3D anti-aliasing and z-buffering.)
Read more about this in detail on nerdplusart.com