H. A. Spencer, or Herbert Alexander Spencer, was a prominent English philosopher and sociologist in the 19th century. He is best known for his contributions to the development of social Darwinism, a theory that applies the concept of natural selection to societies and cultures. Spencer believed that societies evolve over time, much like living organisms, and that this evolution leads to greater complexity and organization. Spencer's work emphasized the importance of individualism and the role of competition in societal progress. He coined the phrase "survival of the fittest," which became widely associated with Charles Darwin's theories, although Spencer used it in a broader social context. His ideas influenced various fields, including sociology, psychology, and education.