He was a rich nobleman that tried to pass some discoveries of one of the Bernoulli brothers as his own, in exchange for cold, hard cash. He was partially successful. Despite this fact becoming broadly known in the math world, a important rule in calculus is still known by his name. See https://en.m.wikipedia.org/wiki/L%27H%C3%B4pital%27s_rule and https://people.math.harvard.edu/~knill/teaching/math1a_2011/...