Leonhard Euler (1707–1783) — say it "OY-ler", not "YOO-ler" — is the most prolific mathematician who ever lived, and quite possibly the most quotable. Pierre-Simon Laplace told his students simply: "Read Euler, read Euler, he is the master of us all." He wrote so much (over 800 papers and books) that the Swiss academy was still publishing his backlog decades after his death.

His notation is the notation

A great deal of the maths you write looks the way it does because Euler decided so. He popularised e for the base of natural logs, i for \sqrt{-1}, \pi in its modern use, \Sigma for sums, and f(x) for a function. He then tied several of them together in what is often voted the most beautiful equation in mathematics — Euler's identity:

His name is scattered across the whole subject: in number theory, Euler's theorem and the totient function; in the calculus of variations, the Euler–Lagrange equation; and in 3-D rotation, the Euler angles. There is a running joke that theorems are named after the second person to discover them, because Euler got to almost everything first.

Blind, and unstoppable

Here is the astonishing part. Euler lost sight in one eye in his thirties and went almost totally blind by sixty — yet his most productive years came after. He simply did the mathematics in his head (his memory was legendary; he could recite the whole of Virgil's Aeneid) and dictated it to assistants. He is said to have produced, on average, a paper a week for much of his life, all while raising thirteen children — reportedly doing mathematics with a baby on his lap and the others playing at his feet.