The biography traces the personal and intellectual development of Ernst Haeckel, following early youth and university training, fieldwork on radiolarians and other marine organisms, adoption and promotion of Darwinian ideas, and the formulation of a general morphology. It combines technical discussion of scientific investigations with episodes of travel, teaching, and public controversy to show how intense idealism and wide-ranging research shaped his career. Illustrated plates and chronological chapters map the growth of his theories, his polemical engagements, and his later years, presenting both specialized findings and the temperament behind his public and professional influence.