Greek philosopher and mathematician. He founded a religious brotherhood, which followed a life of strict asceticism and greatly influenced the development of mathematics and its application to music and astronomy.
from a review of 'The Heretics Feast' by Colin Spencer:
The first prominent modern vegetarian was the Greek philosopher Pythagoras who lived towards the end of the 6th century BC. The Pythagorean diet came to mean an avoidance of the flesh of slaughtered animals. Pythagorean ethics first became a philosophical morality between 490-430 BC with a desire to create a universal and absolute law including injunctions not to kill "living creatures," to abstain from "harsh-sounding bloodshed," in particular animal sacrifice, and "never to eat meat."
As long as man continues to be the ruthless destroyer of lower living beings he will never know health or peace. For as long as men massacre animals, they will kill each other. Indeed, he who sows the seed of murder and pain cannot reap joy and love. - attributed by Ovid
Art & Mathematics - The Pythagoras Tree