The merchant/mathematician Leonardo of Pisa, who was also known as Fibonacci (literally, "son of Bonacci"), was the only European mathematician of note during the Middle Ages. His father was a Pisan merchant who was at one time a customs officer for the North African city of Bugia. Leonardo visited many of the Mediterranean area's centres of learning, including Egypt, Greece, Sicily, and Syria. From these visits he learned the mathematics of the scholars and the calculating schemes in use.
In 1202, he published the first of his four mathematical books, Liber Abaci, which used the Hindu-Arabic number system, introducing the digits 0-9 to Europe. The Muslim influence is clearly demonstrated in his books by the fact that Fibonacci wrote the digits in descending order, and wrote mixed fractions with the fractional part first.
Fibonacci is most famous for the Fibonacci Sequence, a sequence that was named (in the 19th century) for him based on one of the problems in Liber Abaci.