The modularity theorem (formerly called the Taniyama–Shimura conjecture) states that elliptic curves over the field of rational numbers are related to modular forms. Andrew Wiles proved the modularity theorem for semistable elliptic curves, which was enough to imply Fermat’s last theorem. Later, Christophe Breuil, Brian Conrad, Fred Diamond and Richard Taylor extended Wiles’ techniques to prove the full modularity theorem in 2001.

Source: Modularity theorem – Wikipedia