Thomas Hobbes was a 17th-century English philosopher best known for his work in political philosophy. He believed that humans are naturally selfish and that life without a strong government would be chaotic and violent. To avoid this, he argued for a powerful ruler, or a social contract, where people give up some freedoms in exchange for security and order. Hobbes' most famous book, Leviathan, outlines his ideas about human nature and government. He used the metaphor of a sea monster, the Leviathan, to represent a strong state that maintains peace and prevents conflict. His thoughts laid the groundwork for modern political theory.