I don't think ESR had anything to do with egcs directly but, yeah, the egcs/gcc split along with the XEmacs / GNU Emacs fracas were likely inspiration for CatB.

He was always better known as a writer than as a developer - his most significant FOSS contributions were probably fetchmail prior to 2003, and the ill-fated CML2 kernel config system around 2001. I'm not aware of anything of note that he's produced since.

Well, better said would be that ESR was... loud around EGCS? I got into Linux and FOSS essentially just as EGCS took over GCC for good, so I am less clear on details

That's fair! And, yes, he seemed to enjoy rushing into every flamewar he could find back then.

It's one of the reasons this current tweet is so surprising - he's moaning about "drama and politics", "negative useful work", and "shit-stirrers" "who are more annoying to work with than [their] contributions justify", but doesn't seem to realise that all of those complaints could have been made more strongly still about ESR himself, especially when he was in his pomp.