Short answers, pulled from the story.
Friedrich Engels (1820-1895) was a German philosopher, journalist, businessman, and revolutionary socialist. He is best known for co-authoring The Communist Manifesto (1848) with Karl Marx and for developing, alongside Marx, the political and philosophical system known as Marxism. After Marx's death in 1883, he edited and completed the second and third volumes of Das Kapital.
Before his partnership with Marx, Engels wrote Letters from Wuppertal (1839), a critical account of industrial conditions in his home region published under the pseudonym Friedrich Oswald. He also wrote two pamphlets critiquing the philosopher Schelling during his military service in Berlin in 1841-42, and an 1844 article, "Outlines of a Critique of Political Economy", which Marx described as a "brilliant sketch" and which redirected Marx's intellectual focus toward political economy.
Engels worked for two decades as a clerk and eventually a partner at the Manchester cotton firm Ermen & Engels, leading a double life as a respectable businessman and a clandestine communist. Over those years he sent the Marx family in London between £3,000 and £4,000 in total, effectively funding the research and writing of Das Kapital. By 1860 his income had reached over £1,000 a year.
Mary Burns was a young Irish factory worker who became Engels's partner and guide during his first years in Manchester. She escorted him through working-class districts including the Salford slums and the Irish ghetto known as "Little Ireland", areas that would have been unsafe for a bourgeois German to enter alone. Their relationship lasted twenty years until her sudden death in January 1863 and gave Engels direct access to the conditions he documented in The Condition of the Working Class in England.
Critics in the Western Marxist tradition, including György Lukács and Leszek Kołakowski, argued that Engels's application of Hegel's dialectic to the natural sciences in Dialectics of Nature created a rigid, scientistic philosophy later called "dialectical materialism". This framework, they argued, was alien to Marx's more humanistic and historical method, and Herbert Marcuse specifically argued that Dialectics of Nature provided the "skeleton for the Soviet Marxist codification". Engels's defenders, including biographer Tristram Hunt, contend that Stalin explicitly rejected key tenets of Engels's thought and that blaming Engels for Stalinist dogma ignores the political choices of later interpreters.
Published in 1884 and based on Marx's notes on the work of American anthropologist Lewis H. Morgan, the book traces the evolution of the family alongside the development of property relations. Engels argued that the patriarchal, monogamous family was a product of private property and represented what he called the "world historic defeat of the female sex". It became a foundational text of socialist feminism, though it has also been criticised for its over-deterministic materialism and its failure to address the psychological dimensions of patriarchy.