These two guys have several of these historical tales; this one takes us from ed to en to ex to vi, and then to Vim!
Another entertaining video for any “would-be” software historians!
By the way, in the middle of this post, the guy on the right (visually our LEFT), mentions an “illegal” copying of vi at one point in time, though the “illegal” nature is no longer illegal! It’s called Gritter vi, and I have a Version that’s now at Version 4.0. Being once illegal and now “legal”, it’s a pretty faithful implementation of the vi that went to AT&T, as opposed to the updated version of vi that went to BSD, called “nvi”. Guess which one is more efficient and is smaller in size?
(The winner gets an extremely small “prize”): a correct answer! 
Another thing: these guys mentioned mapping keys. The original Escape key on the ADM 3A terminal is where we typically see the CapsLock key today. Well guess what? If you REALLY want that CapsLock key to function the same way the Esc key does you can MAP or remap it to do so AND if you STILL want a Caps lock, you can put that somewhere else (maybe in the labelled Esc key position). Like Emacs, modern vim and nvim have this capability.