Mathematicians ahead of their time? It is said that in every field there’s that person who was years ahead of their time. For instance, Paul Morphy (born 1837) is said to have retired from chess because he found no one to match his technique that very much resembled modern chess theory.
So, who was the Paul Morphy of mathematics?

Simon Stevin (1548 – 1620) had the unbelievable insight of thinking of an arbitrary number in terms of its unending decimal expansion. He was ahead of his time in the sense that the full significance of what he did was not appreciated until the 1870s when more abstract versions of the construction of the reals were given by Charles Méray and others. Unending decimals inspired Newton to introduce more general power series. The rest is history.
Another amazing contribution of Stevin was his argument immediately recognizable as a proof of the intermediate value theorem, which was not "officially" proved until the 1820s by Cauchy. See this article. Here he was ahead of his time by at least 200 years.
