Richard Borcherds proves in 1992, in Inventiones Mathematicae, the "monstrous moonshine" conjecture formulated by John Conway and Simon Norton in 1979, which predicts a deep and seemingly inexplicable relationship between the Monster group — the largest of the sporadic finite simple groups — and the modular j-function, a central object in number theory. Borcherds uses in his proof the formalism of vertex algebras, a tool originating in string theory in theoretical physics, thus establishing an unexpected bridge between finite group theory, number theory, and mathematical physics. Borcherds received the Fields Medal in 1998.