François Viète

A practicing lawyer in Fontenay-le-Comte and royal counsellor at Rennes, Viète served as chief cryptanalyst to King Henry IV during the French Wars of Religion. In 1590, he cracked the complex 500-character cipher used by King Philip II of Spain, leading Philip to accuse Henry of demonic sorcery before the Pope.

In his landmark 1591 treatise In artem analyticem isagoge (Introduction to the Analytic Art), Viète revolutionized mathematics by using vowels for unknowns (A, E, I) and consonants for known quantities (B, C, D), liberating algebra from verbal descriptions into symbolic formulas, directly preparing Descartes and Fermat.