how good of a mathematician was he?
Before he went mad
He was pretty good
Wasn't he supposedly close to solving Fermat's Last Theorem before Wiles
or is that just a myth, i heard it once by someone
absolutely a myth
100% true.
It's what drove him insane
did anyone have him as a professor here?
In a way he is like a genius Elliot Rodgers. You can read about how his anger was caused largely by his lack of success with women, and how he felt they rejected him. He even sent a nasty threatening letter to one. Get your colleagues girlfriends before they start blowing people up.
didn't he also have a deep hatred for his brother or something?
His anger wasn't because of women. He set out on his crusade against modern society because he was hiking in the woods one day and found that some fucker had gone and built a road straight through his favorite bluff.
He was good. There are stories about how he was publishing papers in top journals (solving problems his advisers couldn't) while his classmates were busy working on their homework.
His advisers had no idea he was working on their problems independently. He wouldn't say a word, just pushed the papers on their desk once they were published. Only complaint the profs had was they wish he spoke to them so they could guide him if he were working on problems someone else was etc.
One of his advisers said he was the best he seen.
I don't agree with his message but he wrote a new book
amazon.com