Leonardo Bonacci (c. 1170 – c. 1250), popularly known as Fibonacci or Leonardo of Pisa, was the first great Western mathematician after the decline of Greek science.
His well-known moniker “Fibonacci” is derived from the Latin words “filius Bonacci”, literally translated to “son of Bonacci”. Fi'-Bonacci could be considered the equivalent of the English William-son or John-son.
Fibonacci was born in Pisa, Italy, to Guglielmo Bonacci, a wealthy merchant who directed a trading post at a major port located in present day Algeria. As a boy, Fibonacci accompanied his father on his commercial trips to the Orient. It was during his travels along the Mediterranean coast that the budding mathematician became acquainted with the Hindu-Arabic number system and discovered its enormous practical advantages compared to the Roman numerals, which were still current in Western Europe.
Fibonacci ended his travels around the year 1200 and returned to Pisa. Upon his return, inspired by his interactions with the foreign merchants he met while under the tutelage of his father, Leonardo wrote a number of influential texts that played an important role in reviving ancient mathematical skills. His works garnered him recognition among his contemporaries and high esteem from the reigning Holy Roman Emperor, Frederick II.
His most well-known published book is Liber Abaci (1202), literally translated as “Book of Calculations” or “Book of the Abacus”. The book, which went on to be widely copied and imitated, was based on the arithmetic and algebra that Fibonacci had accumulated during his travels. In it, Fibonacci introduced the so-called modus Indorum (method of the Indians), today known as Arabic numerals and the Hindu-Arabic place-valued decimal system. The book showed the practical importance of the new numeral system by applying it to commercial bookkeeping, conversion of weights and measures, the calculation of interest, money-changing, and other applications. Furthermore, Abaci contains a large collection of problems aimed at merchants. They relate to the price of goods, how to calculate profit on transactions, how to convert between the various currencies in use in Mediterranean countries, and problems which had originated in China. The book was well received throughout educated Europe and had a profound impact on European thought.