Guillaume François Antoine, Marquis de l'Hôpital

Guillaume François Antoine, Marquis de l'Hôpital is perhaps best known for the rule which bears his name for calulating the limiting value of a fraction whose numerator and denominator approach zero.

He is also the author of the first known calculus textbook. Published in 1696, the text includes the lectures of his teacher, Johann Bernoulli, in which Bernoulli discusses the indeterminate form 0/0.