Louis Bachelier

French mathematician credited with being the first person to model the stochastic process now called Brownian motion, which was part of his PhD thesis, "The Theory of Speculation" ("Théorie de la spéculation," published 1900).

His thesis, which discussed the use of Brownian motion to evaluate stock options, is historically the first paper to use advanced mathematics in the study of finance. Thus, Bachelier is considered a pioneer in the study of financial mathematics and stochastic processes.

Defended on 29 March 1900 at the University of Paris, Bachelier's thesis was not well received because it attempted to apply mathematics to an unfamiliar area for mathematicians. However, his instructor, Henri Poincaré, is recorded as having given some positive feedback (though socially insufficient for finding an immediate teaching position in France at that time).

For several years following the successful defence of his thesis, Bachelier further developed the theory of diffusion processes, and was published in prestigious journals. In 1909 he became a "free professor" at the Sorbonne. In 1914, he published a book, Le Jeu, la Chance, et le Hasard (Games, Chance, and Randomness), that sold over six thousand copies. With the support of the Council of the University of Paris, Bachelier was given a permanent professorship at the Sorbonne, but World War I intervened and Bachelier was drafted into the French army as a private.

His army service ended on 31 December 1918. In 1919, he found a position as an assistant professor in Besançon, replacing a regular professor on leave. He married Augustine Jeanne Maillot in September 1920 but was soon widowed. When the professor returned in 1922, Bachelier replaced another professor at Dijon. He moved to Rennes in 1925, but was finally awarded a permanent professorship in 1927 at the University of Besançon, where he worked for 10 years until his retirement.

He died on 28 April 1946, aged 76, in Saint-Servan-sur-Mer, France.