Aelius Galenus, or Galen, was a Greek physician, surgeon and philosopher who lived in the Roman Empire. He is famous for developing the theory of opposites for the Four Humors. Galen added an element to every humor and said that if someone was ill with a cold, they must be fed something hot, and if someone were hot, then fed something cold. He was also famous for discovering more about the human body, or so he thought, by dissecting pigs and different animals. Galen was later proven wrong by Andreas Vesalius, as he was able to dissect human bodies and discover that Galen's work was inaccurate.