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.

[1] Todhunter 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.

[2] Todhunter married 13 August 1864 Louisa Anna Maria, eldest daughter of Captain (afterwards Admiral) George Davies, R.N.

[2] He was a sound Latin and Greek scholar, familiar with French, German, Spanish, Italian, and also Russian, Hebrew, and Sanskrit.

Todhunter wrote textbooks on algebra and trigonometry, and a revision of the translation by Robert Simson of Euclid's Elements, which, with an introduction by Thomas Little Heath, was republished by Everyman in 1933.

[5] Todhunter's major historical works include a history of the Probability theory from the time of Blaise Pascal to that of Pierre-Simon Laplace first published in 1865.