Leonardo Pisano Fibonacci
Leonardo of Pisa, whose nicknames included Fibonacci and Bigolo (meaning "good-for-nothing"). lived c. 1170-1250.
The son of a Pisan merchant, Leonardo was educated in northern Africa, where he became one of Europe's greatest mathemeticians. Surviving publications include Liber abbaci (1202), Practica geometriae (1220), Flos (1225), and Liber quadratorum.
Fibonacci's Liber abbaci was the earliest work to introduce Arabic Numerals (which were actually Hindu on origin) and the use of zero as more than a simple placeholder to Europe. Europe, of course, had little use for academics at the time, and Fibonacci's work was largely ignored until it caught the attention of then-Holy Roman Emperor Frederic II, who invited Fibonacci to his court in 1225.
Although Fibonacci is best known for the so-called Fibonacci Numbers, this is only a small component of the contribution he made to modern mathematics. His publications rescued Europe from the dubious legacy of Roman mathematics, and from the Greek dogmatism against the existence of zero, in effect opening the door for the invention of calculus.