Portrait of Aristotle Courtesy of Corbis-Bettmann.

Aristotle was a Greek philosopher who lived between 384-322 B.C. He was one of the greatest thinkers of the world and his written works encompassed all major areas of thought.

Aristotle mistakenly believed that the Earth was at the center of the universe and made up of only four elements: earth, water, air, and fire. He also thought that celestial bodies such as the sun, moon, and stars, were perfect and divine, and made of a fifth element called ether.