John Thompson, together with Walter Feit, proves in 1963, in a 255-page paper published in Pacific Journal of Mathematics, that every finite group of odd order is solvable — the Burnside conjecture, formulated in 1911 and considered for decades one of the central open problems of finite group theory. The proof, of extraordinary technical complexity for its time, marks the beginning of the classification program for finite simple groups, one of the great collective projects of 20th-century mathematics. Although the result is strictly a joint achievement of Thompson and Feit, only Thompson received the Fields Medal in 1970, since Feit did not meet the prize's age requirement at the time.