Though debated, René Descartes is widely considered to be the father of modern mathematics. His greatest mathematical contribution is known as Cartesian geometry, or analytical geometry.
Descartes' work, "Discours de la méthode," was published in 1637 and was the first to use what has since become standard algebraic practice. His book represented known quantities with the letters "a," "b," and "c," while using the letters "x," "y," and "z" for unknown quantities.
His work with mathematics, physics and philosophy was not approved by the Catholic Church. His works were placed on the Index of Prohibited Books 13 years after his death.