Until the early 1800's vegetarians were commonly known as Pythagoreans, yes, after the ancient Greek mathematician. In those days it could mean with or without eggs and dairy.
Pythagoras was born on the Island of Samos in 569 BC. The details of his life are shady and somewhat mythical. At the tender age of 18 he left Samos and traveled extensively through Europe, Egypt and India, finally settling in Italy and founding a school.
Those who wanted to enter his school had to remain silent in the community for five years before being allowed to contribute their own ideas. The group of men and women were vegetarian, ascetic and believed in reincarnation.
Whilst most famous for his contribution to what is now known as Pythagorean theorem. His group contributed to music, astronomy and philosophy. There are no writings by Pythagoras, so little is actually known of his accomplishments.
But next time someone offers you a sausage you can say "no thanks, I'm a Pythagorean."