Karl Marx


 * Karl Marx: His Life and Teaching, by Zelda Kahan
 * Karl Marx: The Man and His Message, by James Keir Hardie
 * Karl Marx: The Man and His Work, by Karl Dannenberg

Reference works

 * "Karl Marx", in The American Cyclopædia (1879)
 * "Heinrich Karl Marx", in 1911 Encyclopædia Britannica
 * "Karl Marx", in The New International Encyclopædia
 * "Karl Marx", in The New Student's Reference Work