Louis Couturat (January 17, 1868 – August 3, 1914) was a French logician, mathematician, philosopher, and linguist. Born in Ris-Orangis, Essonne, France, he was educated in philosophy and mathematics at the École Normale Supérieure. He held professorships, first at the University of Toulouse, then subsequently at the College de France. He was the French advocate of the symbolic logic that emerged in the years before WWI, thanks to the writings of Charles Sanders Peirce, Giuseppe Peano and his school, and especially to the Principia Mathematica by Alfred North Whitehead and Couturat's friend and correspondent, Bertrand Russell. Like Russell and Whitehead, Couturat saw symbolic logic as a tool to advance both mathematics and the philosophy thereof. In this, he was opposed by Henri Poincare, who took considerable exception to Couturat's efforts to interest the French in symbolic logic. With the benefit of hindsight, we can see that Couturat was in broad agreement with the logicism of Russell and Whitehead, while Poincaré anticipated Brouwer's intuitionism. His first major publication was Couturat (1896). In 1901, he published La Logique de Leibniz, a detailed study of Leibniz the logician, based on his examination of the huge Leibniz Nachlass in Hannover. Even though Leibniz had died in 1716, his Nachlass was cataloged only in 1895. Only then was it possible to determine the extent of Leibniz's unpublished work on logic. In 1903, Couturat published much of that work in another large volume, his Opuscules et Fragments Inedits de Leibniz, containing many of the documents he had examined while writing La Loqique. Couturat was thus the first to appreciate that Leibniz was the greatest logician during the more than 2000 years that separate Aristotle from George Boole and Augustus De Morgan. A significant part of the 20th century Leibniz revival is grounded in Couturat's editorial and exegetical efforts. This work on Leibniz attracted Russell, also the author of a 1900 book on Leibniz, and thus began their professional correspondence and friendship. In 1905, Couturat published a work on logic and the foundations of mathematics (with an appendix on Kant's philosophy of mathematics) which was originally conceived as a translation of Russell's Principles of Mathematics. In the same year, he published L'Algèbre de la logique, a classic introduction to the algebraic logic of George Boole, C.S. Peirce, and Ernst Schroder. In 1907, Couturat helped found the artificial language Ido, an offshoot of Esperanto, and was Ido's principal advocate over the remainder of his life. By advocating an artificial international language, constructed along logical principles and with a vocabulary taken from existing European languages, Couturat was paralleling Peano's advocacy of Interlingua. By pushing Ido, Couturat walked in Leibniz's footsteps; Leibniz called for the creation a universal symbolic and conceptual language he named the characteristica universalis. Couturat, a confirmed pacifist, became one of the very first civilian casualties of World War I, as he was killed when his car was hit by a car carrying orders for the mobilization of the French Army.