Euler's Equation

This is the month of Leonhard Euler's birth; Euler was one of the most prolific, productive mathematicians of all time. His so-called "Euler's Equation" or "Euler's Identity" is considered by many to be hands-down the most beautiful equation in all of mathematics. In his honor this older essay from Keith Devlin:

http://www.maa.org/devlin/devlin_10_04.html