Leonardo of Pisa, who wrote under the pen name Fibonacci, may have been the greatest mathematician of the middle ages. His text Liber Abaci introduced the Hindu-Arabic numeral system to Western Europe in 1202. He is now most remembered for a trivial problem in that text counting the number of offspring of a pair of rabbits. Lucas called the sequence of numbers discussed by that problem the Fibonacci numbers.
See Also: FibonacciNumber