Fibonacci, also known as Leonardo of Pisa, was an Italian mathematician born around 1170. He is best known for introducing the Fibonacci sequence to the Western world through his book "Liber Abaci" in 1202, which details a problem involving rabbit population growth. The sequence is characterized by each number being the sum of the two preceding ones, leading to significant applications in mathematics, nature, and art. Fibonacci's work helped to popularize the Hindu-Arabic numeral system in Europe.