Over at Filmmaker IQ, John Hess narrates a video explaining the long and storied history of aspect ratios, from the invention of 35mm film all the way to modern HD formats. At clocking in at 20 minutes, it’s as complete a history as you’re going to get without calling in Ken Burns to pad things out, and Hess provides a fair amount of technical information as well.
One thing to note in the video and on the Filmmaker IQ website: they fail to make the distinction between 65mm camera negatives and 70mm release prints. The extra 5mm on the print accounts for the film’s soundtrack. It’s a small nitpick, but an important one.