Niels Bohr's life spans times of revolutionary change, in science and in its impact on society. He can be considered, along with Einstein, as the major driving force behind the new mathematical and philosophical descriptions of the atom, the nucleus, and their subsequent repercussions. Abraham Pais, the biographer of Einstein, traces Bohr's progress from his well-to-do origins in late 19th-century Denmark to his central position on the world political scene, particularly because of the development of nuclear weapons during World War II. Bohr was one of the great enabling figures in modern science, not only because of his direct involvement in the application of quantum theory to our understanding of the structure of the atom, but also because he gathered around him in Copenhagen most of the brightest young minds of the period. Figures like Pauli, Dirac, and Heisenberg, all required Bohr's imprimatur, to varying degrees, before they considered their work ready for widespread consumption. He had a complex relationship with Einstein, both in terms of their fundamental disagreements and their profound though distant mutual respect. He owed an important debt to his mentor, Rutherford - a man who came to serve, in many ways, as his role model. Pais describes the state of physics before Bohr and considers his legacy, both theoretical and practical. But more than this, he captures the essence of Bohr, the intensely private family man who, despite appalling personal tragedy, became one of the best-loved cultural figures of recent times.