Mr. and Mrs. Karl MarxActive in the revolution of 1848, Marx fled from Germany in 1849 and settled in London. There Marx and his young wife lived a respectable middle-class life while he wrote Capital, the weighty exposition of his socialist theories. Marx also worked to organize the working class. He earned a modest income as a journalist and received financial support from his coauthor and lifelong friend, Friedrich Engels. (Time Life Pictures/Getty Images)