Leon Thery was born in France on April 16, 1879. He was first employed as a mechanic by Decauville, where he learned to drive. He first raced at the 1899 Paris-Bordeaux race, where he finished in second place behind Fernand Gabriel, who also drove a Decauville. The following years saw him taking part in many races. He was nicknamed “Le Chronometre” because no one else could drive as fast so consistently. After the 1903 Paris Madrid race, he switched to Brasier as a driver, where he was able to reach his zenith. He won the Gordon Bennett races in 1904 and 1905. He then tried to build his own racing car without success. Later, in 1908 he returned to Brasier. He took part in the Grand Prix de France but had to retire while in fourth place. This was his last race. He died of tuberculosis in Paris on March 8, 1909. He was described as “a robust, goodnatured fellow, an excellent mechanician, [who] knows his car thoroughly”.