One can hardly do math without copying Euler. Notations still in use today, such as e and pi, were introduced in Euler's writings. He is perhaps best known for his research into mathematical analysis. Euler's formula cos(x) + isin(x) = e (ix) demonstrates the relationship between algebra, complex analysis, and trigonometry. From this equation, it's easy to derive the equation e(pi i) + 1 = 0 which relates the fundamental constants: 0, 1, pi, e, and i in a single beautiful and elegant statement. Leonhard Euler died in 1783, leaving behind a legacy perhaps unmatched, and certainly unsurpassed, in the annals of mathematics. Math 895: The History of Mathematics