Henri Lebesgue - Wikipedia, the free encyclopedia

He actually rewrote calculus, and finally got it exactly correct, long after Newton and Leibniz, or Leibnitz, I was never certain of the spelling. He invented measure theory, central to understanding differentiation and integration in calculus, especially involving irrational numbers, as well as central to probability theory. I only mention him, as, basically, few even know of him now, enjoy.