Lewis Morgan was a prominent 19th-century American anthropologist and social theorist, known for his work on the development of human societies. He is best recognized for his book, Ancient Society, published in 1877, where he introduced the concept of social evolution, categorizing societies into stages: savagery, barbarism, and civilization. Morgan's research focused on the Iroquois people, which greatly influenced his theories on kinship and social structure. He is often credited with laying the groundwork for modern anthropology and sociology, and his ideas have had a lasting impact on the study of human cultures and social organization.