Louis Jean-Baptiste Alphonse Bachelier (French: [ba??lje]; March 11, 1870 – April 28, 1946) was a French mathematician at the turn of the 20th century.
He is credited with being the first person to model the stochastic process now called Brownian motion, as part of his PhD thesis The Theory of Speculation (Théorie de la spéculation, published 1900).
Bachelier's Doctoral thesis, which introduced for the first time a mathematical model of Brownian motion and its use for valuing stock options, is historically the first paper to use advanced mathematics in the study of finance.
Thus, Bachelier is considered as the forefather of mathematical finance and a pioneer in the study of stochastic processes.