Cyclops

Leonhard Euler produced 866 mathematical papers, gave us the letters e, i, π, and the notation f(x), and proved that the sum of the reciprocals of the squares of the integers converges to π²/6. Frederick the Great called him "my Cyclops," on account of the one working eye.

In 1771 a cataract surgery briefly restored his sight. Then it went septic and he went totally blind.

By 1775 he was dictating a paper a week. He dictated equations in chalk on a large slate while a child bounced on his knee and, per one witness, a cat sat on his shoulders. When two students calculated a slowly converging series and disagreed at the fiftieth decimal place, blind Euler ran through it in his head and gave the correct value. He also had Virgil's Aeneid in there, all 9,896 lines of it, so there was room.

On 18 September 1783 he chalked balloon-ascent equations on the slate, took lunch with the astronomer Lexell to discuss the newly discovered planet, Herschel, played with another grandchild, and lit a pipe. The pipe slipped from his hand.

He ceased to calculate and to live.