Diophantus

Diophantus of Alexandria was an ancient Greek mathematician. He is well known for his series of books called "Arithmetica". He mainly focused on solving algebraic equations. His work was built upon by Pierre de Fermat, a French mathematician, who claimed that a certain equation created by Diophantus was unsolvable. The attempts to prove this claim, now known as Fermat's Last Theorem, led to major advances in number theory.
Biography.
Not much is known of Diophantus's life. Some information is given by another Greek mathematician, Metroduros, through various problems that he wrote which supposedly contained hints about Diophantus' life. 
"Arithmetica".
Diophantus' main notable work is his series of books called "Arithmetica." It is a collection of problems and solutions to those problems. These problems have come to be known as Diophantine equations. The method in which they are solved is now called Diophantine analysis.