Today, the 15th of April, is Euler’s birthday. Euler, a pioneer of modern mathematics, was born on April 15 1707, in Basel, Switzerland. His work introduced much of today’s modern notation. He worked on quite diverse areas such as mathematical analysis, geometry, number theory, graph theory and so on, as well as making massive impact in the world of physics in areas such as mechanics and optics.
Portrait by Johann Georg Brucker (1756)
Euler Biography (The MacTutor History of Mathematics archive)