MathOverflow user who has asked the most HNQs is Tim Campion with 36 questions.

If we look at the most answers to HNQs, Carlo Beenakker has 163 of them.

@MartinSleziak I have to imagine there's some recency bias here -- there must have been a time when HNQ didn't exist or else when MO was not eligible for HNQ. I wonder what the history is...

The same queries used on meta return Hot Meta Posts: Askers, Answerers.

@TimCampion Entering HNQs is recorded in the timeline and revision history only since February 2019: Now you can know if a question really hit the HNQ.

So the data before that are not available in SEDE.