Likely Jim Watkins or his son Ron Watkins, the owner and the administrator of 8kun. But it could also be someone working with them. It's hard to prove who is Q. What's easier to prove is who controls Q. Q made his posts platform dependent for seemingly no reason in the post about "no outside comms". A competent government agent would be able to use a cryptographic signature to establish his identity across multiple platforms without relying on a porn filled imageboard's flimsy tripcodes. Q explicitly tied himself down to 8chan, which later go reinterpreted to mean any derivative website owned by Jim Watkins, right now that means 8kun.top. A competent government agent would not limit their options like that. If Qanon was ever someone other than Jim Watkins while he was on 8chan, then it's likely that Jim Watkins stopped qanon from establishing platform independence, by either filtering his posts and allowing only approved posts or by directly taking the tripcode or changing the content of messages.
Jim Watkins has a motivation to be qanon. Qanon drives lots of traffic, millions of impressions a month and that can be monetized.
The Watkins' decided who was the "legitimate" qanon when there was a break in the chain of tripcodes.