Diophantus was a mathematician from Alexandria in ancient Greece. He lived sometime around 250 AD but giving exact dates is extremely difficult. No-one really knows for sure.

Diophantus was interested in solving polynomial equations with integer or rational equations. We now call these Diophantine equations.

The most famous Diophantine equation of them all is xn+yn=zn and Fermat's notorious marginal note

I have discovered a truly remarkable proof which this margin is too small to contain
was written in his copy of Diophantus' Arithmetica.

See also the proof of Diophantus' theorem on Pythagorean triples and Fermat's Last Theorem.