Leonardo of Pisa

Italian mathematician, widely known by the nineteenth century nickname Fibonacci, who introduced the Hindu-Arabic numeral system to Europe through his 1202 book Liber Abaci, replacing cumbersome Roman numerals with the positional decimal system still used today. The same book poses a rabbit-breeding problem whose solution is the sequence, later named after him, in which each number is the sum of the two before it; the sequence and its connection to the golden ratio became far more famous in later centuries than Fibonacci himself.