Pythagoras was an ancient greek are a. historian b. mathematican c. physician d. ruler

  B. Mathematician

Explanation:  Pythagoras was a Greek mathematician from the period of ancient Greece, also a philosopher. He interpreted the entire physical world, the proportions in space, nature, and architecture, using the numbers, considered the meaning of the numbers very important for the proportions of the objects in architecture. He is best known for the theory of a right-angled triangle, the so-called Pythagoras theorem.