Friedrich Engels was a German philosopher, social scientist, journalist, and businessman. He founded Marxist theory together with Karl Marx. In 1845, he published The Condition of the Working Class in England, based on personal observations and research in Manchester. In 1848, he co-authored The Communist Manifesto with Karl Marx, though he also authored and co-authored many other works, and later he supported Marx financially to do research and write Das Kapital. After Marx's death, Engels edited the second and third volumes. Additionally, Engels organised Marx's notes on the Theories of Surplus Value, which he later published as the "fourth volume" of Capital. He also made contributions to family economics.

https://en.wikipedia.org/wiki/Friedrich_Engels