Aristotle was a 4th century BCE Greek philosopher whose books have become a integral part of university curriculum on western philosophy. Aristotle was a disciple of Plato, also a Greek philosopher.
Aristotle has written books that expounded on his philosophies. One of his more known concepts was the idea of classifying human beings as "social rational animals" - ie. that humans are intelligent/thinking social animals who need to be in a community with other human animals in order to be well.