Interesting thread.
Before anything more, let me say this:
There are so many people that have contributed an incredible amount of time, effort, and work for ASL in countless different ways for the benefit of many or all, that it would do these injustice not to acknowledge them, though it would be next to impossible to compile a complete list that gives credit to all those that deserve it.
Yet, there are some who do stand out
I will attempt to approach the OP's question not from an overall perspective but from the current point in time:
The crown would go to the VASL and VASSAL crew:
Doug Rimmer, Al Cannamore, Tom Repetti, Brian Kemp, David Sullivan, Joel Uckelman, and the map elves, code gnomes, and counter trolls that support them.
Their work unites the ASL world-community more than anything else. Just think of the Corona-times without VASL. Numerous tournaments have under the given circumstances switched to VASL to make something happen. For sure, VASSAL and VASL have been the tools to really make ASL come alive to me. All of a sudden, I had opponents and mentors to play around the world and around the clock if I so desired. What they have created bridges anything that might be out of print or just out of reach. VASSAL/VASL are simply the prime enablers that can easily bring players together worldwide at no cost. Their impact on ASL cannot be overstated.
Next rank for me the rules gurus that display the endless patience and knowledge to explain the most obscure questions of the tremedously complex rules again and again and again - and again:
The most outstanding of these are - at least since I am around since 2010 - Klas Malmström (who also created and maintains the priceless Q&A compilation) and JR van Mechelen (also responsible for ROAR, a prime ASL resource), who - unfortunately has left this forum in anger a while ago. Would, if he returned. There are more of tremendous rules knowledge and commitment, but the objective of the OP is to keep the list short.
Third rank for me the "officials":
Perry, Brian, Chas. You've got to have somebody, who keeps the heart of the system running.
Interestingly, though, I am convinced, that even if MMP would not exist anymore and some evil force stopped all its publications inclusive of the rulebook, ASL would not die.
Fourth come those that maintain the most valuable tools/gadgets around ASL:
Which means, that some receive a double credit.
The Q&A compilations by Klas Malmström.
ROAR by JR van Mechelen.
Gamesquad Forum, i.e. formerly "Dr. Zaius" and now "RandyT0001"
The ASL Scenario Archive by Dave Ramsey and some prime supporters that relentlessly fill it with additional information.
AREA and the new AREA
The Texas ASL Club website which might be the prime source for downloads of all sorts of ASL stuff
Desperation Morale Website by Mark Pitcavage
Paul Weir - he is a "gadget" in himself: The walking library of AFV-knowledge...
Fifth come the Tournament Directors and organizers:
The most pleasant ASL experiences you can have is getting together with a bunch of freaks in real life. Best place to learn. Best place to look at other peoples gadgets, storage systems, ynkelonium-terkonite tweezers that would even work in an anti-matter environment, etc. Best place to socialize with ASLers and to strike friendships some of which might last forever.
Sixth come the Scenario Designers and CG-Developers:
Two decades ago, I probably would have ranked these higher. After all, you need people who create the stuff we play. But with safely 6000 scenarios around (having already subtracted clones, reissues and rehashes), there is so much stuff in existence (though not in print - I concede that), that practically no one could ever play all of it in a lifetime.
Seventh come the mentors and teachers:
You can try to learn ASL from the rulebook. I did. For lack of opponents before VASL. You won't get very far no matter how long you try if you play solitaire or always vs. the same opponent. You need people to teach you, who sort of act as mentors, that show patience and take time to explain when you do not know and have not grasped parts of the rules yet - and who kick your carboard soldiers' butt, so that you remember the lesson. These people will save you years of time by what they do and make ASL so much more enjoyable. Every experienced ASL-player will be able to name some. The aforementioned late Patrick Ireland surely stands out as one who took care of the absolutely rare recruits for their very first games / VASL experiences.
Eigth come the siginifcant others that tolerate our capers:
Inspired by Actionjick, I had to add them. If they wouldn't put up with our childs-play, ASLers couldn't play or contribute. It must be hard to endure grown men making tank noises, ordering yet another box full of cardboard that almost looks like all the others for 150 $ upwards apiece, clipping countless counters (for what ?!), adding yet more pounds while attending those 'tournaments' (wasn't that supposed to be something about knights to impress ladies by jousting?) by gobbling down fast-food since 'there is no time for a real meal'.
At this point, I will not continue my list despite it could go one for quite a bit. Writing the above, I realized how difficult it is to put single names to the individual topics.
von Marwitz