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.