He won the fields medal, which is the effectively the Nobel prize for math, and has been cited nearly 100k times. Academically, these are extremely high level achievements. He’s contributed across very diverse fields of math, so it’s difficult to pin down his contributions to one thing in particular, but his most cited papers are fundamental to compressed sensing, which is both theoretically interesting and practically useful
Off the top of my head, two big accomplishments are compressed sensing and the existence of arbitrarily long arithmetic progressions in the primes (the Green-Tao Theorem, https://en.wikipedia.org/wiki/Green–Tao_theorem). But there is more than that. It’s a very googleable question.