Euler, Leonhard (1707-83), Swiss mathematician, whose major work was done in the field of pure mathematics, a field that he helped to found. Euler was born in Basel and studied at the University of Basel under the Swiss mathematician Johann Bernoulli, obtaining his master's degree at the age of 16. In 1727, at the invitation of Catherine I, empress of Russia, Euler became a member of the faculty of the Academy of Sciences in Saint Petersburg. He was appointed professor of physics in 1730 and professor of mathematics in 1733. In 1741 he became ....