Friedrich Engels was a German philosopher, social scientist, and businessman who is best known for his collaboration with Karl Marx. Together, they co-authored "The Communist Manifesto" and "Das Kapital," which laid the foundation for the socialist and communist movements. Engels was a prominent figure in the early development of Marxist theory and played a key role in shaping the ideology of communism. He also contributed to the fields of economics, sociology, and history, and his work continues to influence political and social thought to this day.