Bad ass Mathematician from back in the day

Augustin-Luis Cauchy(1789-1857)

It's interesting to learn how the great minds of the past came up with the ideas that are still relevant today. Among these is Augustin Cauchy, who gave rigor to Calculus.

How in the world was Calculus invented?


If you are interested in this question
Who gave You the Epsilon? Cauchy and the Origins of Rigorous Calculus (pdf) by Judith V. Grabiner gives a good answer to that.