Fibonacci was an Italian mathematician born around 1175 in Pisa who popularized the Hindu-Arabic numeral system in Europe through his 1202 book Liber Abaci. The book advocated using the numerals 0-9 with place value, making calculations easier and faster. It discussed applications in commercial accounting. Fibonacci also introduced the Fibonacci sequence and irrational numbers. He travelled extensively, learning about new mathematical systems before popularizing the more efficient Hindu-Arabic system in Europe.