Leonhard Euler (April 15th, 1707 - September 18th, 1783) was a Swiss mathematician and physicist. He developed the theory of differential equations, the calculus of variations, and did important work in astronomy and optics. A pupil of Johann Bernoulli, he became professor of physics at the University of St Petersburg, Russian, in 1730. In 1741 he was invited to Berlin by Frederick the Great, where he spent 25 years before returning to Russia. He was totally blind in the last years of his life, but an ability to calculate in his head ensured that his productivity did not diminish. He published 800 papers, contributing to all areas of mathematics. A statement attributed to Laplace expresses Euler's influence on mathematics: "Read Euler, read Euler, he is the master of us all." 1783, after a lunch with his family, Euler was discussing the newly discovered planet Uranus and its orbit with a fellow academician Anders Johan Lexell, when he collapsed from a brain hemorrhage. He died a few hours later at the age of 76. Engraving from "Vies des savants illustres" by Louis Figuier.