Herbert Alexander Spencer (1820-1903) was an English philosopher and sociologist known for his contributions to the development of social theory. He is best recognized for coining the phrase "survival of the fittest," which he applied to social evolution, suggesting that societies evolve in a manner similar to biological organisms. His ideas influenced various fields, including sociology, psychology, and political theory. Spencer's work emphasized the importance of individualism and the role of competition in societal progress. He wrote extensively, with notable works such as The Principles of Sociology and Education: Intellectual, Moral, and Physical. His theories laid the groundwork for later thinkers, including Charles Darwin and Emile Durkheim.