The author of the book Das Kapital is Karl Marx, with assistance from Friedrich Engels. The solutions to the crossword are KARL (4 letters), MARX (4 letters), ENGELS (6 letters), ERDA (4 letters), ENDE (4 letters), ERDE (4 letters), and KARLMARX (8 letters). Karl Marx was a German philosopher, economist, historian, sociologist, political theorist, journalist and revolutionary socialist who developed the socio-political theory of Marxism. Friedrich Engels was a German philosopher, communist, social scientist, journalist and businessman. He founded Marxist theory together with Karl Marx.