+ From Wikipedia: "Friedrich Engels was a German social scientist, author, political theorist, philosopher, and father of Marxist theory, alongside Karl Marx. In 1845 he published The Condition of the Working Class in England, based on personal observations and research. In 1848 he co-authored The Communist Manifesto with Karl Marx, 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 organized Marx's notes on the "Theories of Surplus Value" and this was later published as the "fourth volume" of Capital. He has also made important contributions to family economics."