Leonardo Fibonacci was an Italian mathematician born around 1170 in Pisa. He is best known for introducing the Fibonacci sequence, a series of numbers where each number is the sum of the two preceding ones, starting from 0 and 1. This sequence appears in various natural phenomena, such as the arrangement of leaves and the branching of trees. Fibonacci's most famous work, the book Liber Abaci, published in 1202, introduced the Hindu-Arabic numeral system to Europe, replacing the Roman numeral system. His contributions significantly influenced mathematics and helped lay the groundwork for modern arithmetic and number theory.