Hipaso de Metaponto was a 6th century BC Greek mathematician and philosopher born in Metaponto, Italy who was a member of Pythagoras' school. He is believed to have discovered irrational numbers, contradicting the Pythagorean belief that all things were rational, and was expelled from the school as a result. The circumstances of his later death are uncertain but may have involved a shipwreck, suicide, or murder by Pythagoreans.