The present biography, originally published by dtv, portrays the founder of critical rationalism as a complex personality and the profile of a modern enlightener who throughout his life strived for a scientific as well as humanitarian mindset. As a theorist of science, Popper emphasized the central importance of an experience-oriented, critical examination of theories, and as a political thinker, he highlighted the crucial role of criticism for what he called the "open society." In doing so, he significantly shaped both the modern understanding of science and our concept of democracy. The book includes a new chapter on "Popper's Legacy in the Present.".