Who are you, Monsieur Le Blanc?

The famous Ecole Polytechnique opened in 1794 in Paris was reserved only for men. As usual, some of the students were slovens. Among such slovens was Antoine-August Le Blanc. A special eagerness to learning, he did not show.
Professor Lagrange, who was reading analysis course at the Ecole Polytechnique, requires that the students write weekly assignments on selected problems. Recently, a special attention of Lagrange began to cause the answer sheets signed by the name of «A.-A. Le Blanc». Professor could no longer ignore the brilliance of Monsieur Le Blanc’s answer sheets. Not only were Monsieur Le Blanc’s solutions marvelously ingenious but they showed a remarkable transformation in a student who had previously been notorious for his abysmal mathematical skills. Lagrange requested a meeting with the reformed student.
What happened next, and who is hiding under the pseudonym "Monsieur Le Blanc", you will know from the talk.