In 1900, in a Paris doctoral thesis that almost nobody wanted to supervise, an unknown student named Louis Bachelier (1870–1946) modelled the random wiggle of stock prices on the Paris Bourse using what we now call Brownian motion — five years before Einstein used the very same maths to explain jittering pollen. Bachelier invented mathematical finance. For his trouble he got, essentially, a polite B.

Ahead of his time, to a fault

His examiner was Henri Poincaré — a genuine giant — who admired the originality but couldn't quite get past the topic. Money? A slightly disreputable thing to point serious mathematics at. The thesis earned "honorable" rather than the top "très honorable", and that soft grade quietly capped Bachelier's career. He drifted through minor teaching posts, was once knocked back over a misunderstood sign in a formula, and his masterpiece sat on a shelf gathering dust for half a century.

Rediscovered, about a century late

In the 1950s the economist Paul Samuelson tripped over Bachelier's forgotten thesis and realised it was decades ahead of everyone in the room. It became the seed of the random-walk model of markets and, in time, of the Black–Scholes formula — the work that Itô and Wiener gave the rigorous foundations for. The original quant finally got his due, having been right roughly a hundred years too early.

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The full story (with far fewer jokes) is on Wikipedia: Louis Bachelier — Wikipedia.