That's the same guy that posts as @graycat here on HN. Most of his posts espouse the wonders of hardcore applied math, often with a comprehensive bibliography, so he seems to know what he's talking about, although his rambling (and, to be fair, somewhat off-topic) style does him no favors on HN, which is why his posts almost always end up at the bottom of the comments here (see also @michaelochurch).

Michael O. Church got modded off of HN for being critical of certain aspects of YC (according to him).

You can see for yourself why he was banned: https://news.ycombinator.com/item?id=10017538

True, but it's more b/c his criticism of VC and PG specifically has a Captain Ahab level of intensity and persistence, which can get in the way of discussing, well, anything else.

Exactly, which is why I made the connection.

Still, the "single-issue commenter", as exemplified by both of them, can be valuable to a good community. @michaelochurch's writings have definitely shaped my thoughts, so kudos for him, and, if I were in the position to use it, @graycat's bibliographies would be rewarding to mine (unless his knowledge is outdated, as @barrkel suggests). Yet I can't help but get the impression that the single-issue commenter is very prone to overexposing themself, especially if a large proportion of their comments are multi-thousand word diatribes that recycle most of the same themes. Not to mention, people readily pattern-match prolix commenters to complete crackpots, even though both those users seem to be above that level. My impression is that single-issue commenters would be best served by posting a lot for a year or so, followed by some time to lie low -- if their contributions to the discussion around their issue are really valuable, their posts should stay in moderate circulation as other users refer to them in later discussion.

He displays a lot of knowledge, but also doesn't look fully mentally with it. He has trouble controlling verbosity and keeping things relevant and on-topic. It's also not clear how much up to date knowledge he has; he writes like an old man complaining about the foolish optimism of youth.