John Wallis

John Wallis (1616 to 1703) was an English clergyman and mathematician who is given partial credit for the development of infinitesimal calculus and who also served as chief cryptographer for Parliament and, later, the royal court between 1643 and 1689. He studied at Emmanuel College, Cambridge, and in 1649 was appointed Savilian Professor of Geometry at Oxford, a post he held for 54 years. His cryptographic work came at a time when cipher design was poorly understood and most ciphers were ad hoc methods relying on a secret algorithm; he realised that systems based on a variable key were far more secure, though he refused Leibniz's request of 1697 to teach Hanoverian students about cryptography. His most important mathematical work, Arithmetica Infinitorum, was published in 1656, and he is credited with introducing the symbol for infinity.