Pythagoras was an influential ancient Greek mathematician and philosopher born on the island of Samos in the 6th century BCE. He founded a school of philosophy called the Pythagoreans in Croton, Italy, where he established strict rules for his followers to live by. Pythagoras is best known for discovering the Pythagorean theorem, which states that in a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides. Little is definitively known about Pythagoras's life and mathematical achievements due to the secrecy of his society and lack of surviving writings.