The French Defense derives it's name from a correspondence game played between London and Paris (1834-1836), won by the Parisians of course.
The French was introduced into master practice in the early 1800s by (who else?) a Frenchman, La Bourdonnais. I. A. Horowitz also credits Geza Maroczy with helping to popularize its use beginning around the end of the 19th century. No less an authority than former World Champion Mikhail Botvinnik however, opines that the real history of the French Defense began with Aaron Nimzowitsch, who contributed many new ideas, and for whom a major variation of the French Defense was named. Many World Champions, as well as other strong GMs, have wielded the French as a weapon during their careers, including Karpov, Botvinnik, Korchnoi, Smyslov, Bronstein, Petrosian, Uhlmann, Capablanca, Reti, Grunfeld, and Alekhine. More recently, the French has been essayed by the likes of Anand, Khalifman, Short, Bareev, Van Wely, and Ivanchuk, to name just a few.