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 always curious to see what he's been up to!

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.