"your impression", is true only in the Ruliad. Ask people who knew him back in the 80's... he never worked on anything on his own that has amounted to anything. He is a real life crank, crackpot and all around charlatan.

Mathematica is the product of 30 years of work on Macsyma and Maple systems at MIT and elsewhere, which he cracked its codebase, usurped and sold to an unsuspecting academic community back when only the likes of Bill Gates would do such as thing.

He also missed the entire LLM wave because he refused to open source WolframAlpha codebase and work with others in the NLP community.

So, ah, my "full of fantasies of unlimited success and fame" was not derogatory enough for your tastes, then?

any specific source ? (fire time I hear that about Wolfram )

My impression is based on hearing him speak for a few hours and maybe some biographical facts such as can be gotten from Wikipedia.