Arthur Cayley (August 16, 1821 - January 26, 1895) was an English mathematician who helped found the modern British school of pure mathematics. He entered Trinity College, Cambridge, where he excelled in Greek, French, German, and Italian, as well as mathematics. He worked as a lawyer for 14 years. He postulated the Cayley-Hamilton theorem, that every square matrix is a root of its own characteristic polynomial, and verified it for matrices of order 2 and 3. He was the first to define the concept of a group in the modern way as a set with a binary operation satisfying certain laws. In 1876 he published a Treatise on Elliptic Functions, which was his only book. In 1889 the Cambridge University Press requested him to prepare his mathematical papers for publication in a collected form. While editing these volumes, he succumbed to a painful internal malady, and died in 1895, at the age of 74.