There’s a long simmering debate among hardcore Emacsistas about who what did what in the initial development of Emacs. Most of us know that Emacs began as a curated set of editing macros for the TECO editor. At the MIT AI Lab where all this happened back in 1976, virtually everybody used TECO but they all had their own set of macros.
In order to bring a little rationality to chaos, RMS and Guy Steele decided to select the best macros and offer them as a standard macro set. When you put it that way it doesn’t seem like much of an effort but there as a lot of work by a lot of people just to get things running the way they wanted them to.
All this was almost 50 years ago so of course memories are dim and there are disputes as to who was involved and how much they did. Jeremy Bryant has an interesting blog that considers Emacs, Lisp, and related matters. One of his entries considers the origin of Emacs. To some extent it depends on the recollections of those involved but Steele had a bunch of emails that he contributed to a long thread on Dan Weinreb’s blog.
The TL;DR is that RMS did most of the heavy lifting almost from the beginning. For the first few weeks Steele was heavily involved as were others. Take a look at the blog for the details. A lot of the discussion presumes a knowledge of TECO and its macro system but it’s possible to figure what was going on and who the major players were.
Emacs evolved significantly from those seeds and again RMS put in a huge amount of work. No Emacs user needs to know any of this, of course, but hard core Emacsers will probably find it interesting.