Isaac Todhunter FRS (23 November 1820 – 1 March 1884), was an English mathematician who is best known today for the books he wrote on mathematics and its history. The son of George Todhunter, a Nonconformist minister, and Mary née Hume, he was born at Rye, Sussex. He was educated at Hastings, where his mother had opened a school after the death of his father in 1826. He became an assistant master at a school at Peckham, attending at the same time evening classes at the University College, London where he was influenced by Augustus De Morgan. In 1842 he obtained a mathematical scholarship and graduated as B.A. at London University, where he was awarded the gold medal on the M.A. examination. About this time he became mathematical master at a school at Wimbledon. In 1844 Todhunter entered St John's College, Cambridge, where he was senior wrangler in 1848, and gained the first Smith's prize and the Burney prize; and in 1849 he was elected to a fellowship, and began his life of college lecturer and private tutor.[1] In 1862 he was made a fellow of the Royal Society,[2] and in 1865 a member of the Mathematical Society of London. In 1871 he gained the Adams prize and was elected to the council of the Royal Society. He was elected honorary fellow of St John's in 1874, having resigned his fellowship on his marriage in 1864. In 1880 his eyesight began to fail, and shortly afterwards he was attacked with paralysis. Todhunter married 13 August 1864 to Louisa Anna Maria, eldest daughter of Captain (afterwards Admiral) George Davies, R.N. (at that time head of the county constabulary force). He died on 1 March 1884, at his residence, 6 Brookside, Cambridge. A mural tablet and medallion portrait were placed in the ante-chapel of his college by his widow, who, with four sons and one daughter, survived him. He was a sound Latin and Greek scholar, familiar with French, German, Spanish, Italian, and also Russian, Hebrew, and Sanscrit. He was well versed in the history of philosophy, and on three occasions acted as examiner for the moral sciences tripos. An unfinished work, The History of the Theory of Elasticity, was edited and published posthumously in 1886 by Karl Pearson. Todhunter also published keys to the problems in his textbooks on algebra and trigonometry; and a biographical work on William Whewell (1876), in addition to many original papers in scientific journals. Some of these are available at Isaac Todhunter's publications at Google Books. This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain. This article incorporates text from the entry Todhunter, Isaac in the Dictionary of National Biography (1885–1900), a publication now in the public domain.