I've only been using Emacs for 7 or 8 years, but in my admittedly limited experience, Protesilaos has singlehandedly done more to bring more people into the community than anyone. He's been a huge advocate for composability in packages, through use of the core Emacs functions, allowing incredible flexibility without being locked into a particular library (e.g. Helm / Ivy).
I'm unashamedly singing Prot's praises below there, but I must say, there are many, many people who've done amazing things to bring people in to Emacs over the last few years. Singling one person out as doing "the most" is in my opinion not sensible or fair.
Without reflecting much at all or trawling through various resources, Mike Zamansky, Sacha Chu, Mickey Peterson, etc etc. Not to mention all the maintainers, Eli Zaretskii, Lars Ingebrigsten, and however many others I don't know about, loads probably.
Prot continuing to be thorough in his work, write clearly, and produce very useful stuff for Emacs operators. This guide looks very interesting (even for slightly-above-beginner Emacsers like myself).
- "Having observed beginners [sic] struggle with C-g not closing the open minibuffer, I know that the following is a quality-of-life refinement:"
Oh wow does this one make me feel stupid. I've spent eons doing a C-x o C-x o C-x o... dance every time there's some bugging-out minibuffer prompt. It *never once* occurred to me to reflect on that as a "I'm doing it wrong!" issue.
That one was tricky to figure out for me, too. I had a colleague ready to give up on Emacs because of that very issue.
Myself, I also haven't thought about fixing `C-g`. I ended up settling on a compromise solution - I have `winum` package configured so that pressing `M-0` focuses minibuffer, if open, so closing defocused minibuffer is just `M-0 C-g` for me. The keys `M-1` through `M-9` focus the windows 1 through 9, as usual.
I'm always curious to see what he's been up to!