Perelman provided a proof of the Poincare Conjecture, which had stumped mathematicians for a century.
It was also one of the seven Millenium problems https://www.claymath.org/millennium-problems/, and as of 2024, the only one to be solved.
Andrew Wiles became pretty well known after proving Fermat's last theorem, despite there not being an financial reward.
Granted, we're not on a forum where most people go, so I shouldn't have said "you" in that case.