Very good question - I had similar issues
In the first instance, it is a good thing. What you need are more people like him, so the objective is not to hold him back, but to attract others who are like him.
If, as you say, he enjoys the community - and not just the personal attention (as someone else was struggling with) he will completely understand if you contact him to discuss this issue. By involving him in an informal ambassador / moderator / community-builder role you have the opportunity to make him even more committed, but possibly also more constructive.
I would contact him, explain that the community will be healthier (!) if TOGETHER you can encourage more people to participate and that maybe he could refrain from posting on occasion to give space for others to comment.
The most eager members, and staff, need to take a moment to ‘stand back’ and be ‘active’ not just in speaking/participating, but in encouraging others to speak and participate. I suspect he doesn’t see the issue, and by pointing it out, you can get him onside.
My own issue then became a bit larger because it was a group of members doing this, and most of them were men, so I additionally had the issue that the first response was often from a similar perspective. I am still working on this, but as we add more members the effect becomes less pronounced, so I am not as worried about it even if I am still working to improve it.