For him the smallest particles were the greatest: Werner Heisenberg, one of the founders of quantum mechanics. Few physics Nobel Prize winners forged such intense links with the Lindau Meetings. He came here to Lake Constance 15 times. The exchange with his peers and young scientists was a reason to keep coming. But who was this man, a genius and controversial figure, who decisively influenced the course of physics in the 20th century? Werner Karl Heisenberg was born on 5 December 1901 to Dr. August Heisenberg and Annie Wecklein in Würzburg. When he was eight years old the family moved to Munich. There his mathematical talent soon became apparent. He was also gifted musically. Playing the piano would become a lifelong passion. After completing school as a brilliant pupil, Heisenberg enrolled at the University of Munich where he studied theoretical physics under Arnold Sommerfeld, a pioneer of atomic theory. From the start Heisenberg was fascinated by questions of philosophical scope. Sommerfeld recognized the talent of his student and arranged for him to meet Niels Bohr. The encounter was a decisive event for the young Heisenberg and marked the start of his scientific development. After three years of study Heisenberg submitted an outstanding doctoral thesis which however due to differences with the experimental physicist Wilhelm Wien only received a passing grade. That setback did not however harm Heisenberg’s career and he became assistant to Max Born at the University of Göttingen receiving his “habilitation” a year later. In 1925 he made his most significant contribution to physics, the mathematical foundations of quantum mechanics. His view was that in measuring a system we impact it, that humans are the co-creators of their own reality. It was a completely new way of looking at things and a theoretical breakthrough in atomic physics. Expanding his idea together with Max Born and Pascual Jordan he produced the first mathematical formulation of quantum-mechanical phenomena. The tireless work and many discussions on the new theory led him in 1927 to what is now called the Heisenberg uncertainty principle, still one of the most important rules of quantum mechanics. This new understanding of the world of the smallest particles continues to be of immense importance in physics. But this period of upheaval was a difficult one. Quantum mechanics is the most successful of all the frameworks that we have discovered to describe physical reality. It works, it makes sense and it is hard to modify. Some of the boldest pioneers of quantum mechanics notably Einstein, resisted the replacement of classical determinism with a theory that can often only make probabilistic predictions. And even harder to get used to was the idea that in quantum mechanics one can describe a system in many incompatible different ways. There is no unique exhaustive description. Even a pioneer of quantum physics like Albert Einstein had his problems with the concepts, especially with the philosophical consequences. He is often quoted as saying: “I am convinced that God does not throw dice.” At the age of 26 Heisenberg was a star in the physics firmament and was appointed professor of theoretical physics at Leipzig University. He was at the high point of his career. In 1932 he received the Nobel Prize for his work in creating quantum mechanics. Soon after he met his wife Elisabeth Schumacher with whom he would go on to have seven children. But this was also a dark time. When the Nazis came to power, many scientists left Germany. Werner Heisenberg stayed –an ambiguous situation. On the one hand he was criticized for working for the Nazis. On the other hand he also met with hostility in Germany; his work was attacked as ‘Jewish physics’. Heisenberg felt isolated, both academically and socially. The discovery of nuclear fission suddenly made modern physics interesting to the Nazis. Werner Heisenberg and other scientists were drafted into the so-called “uranium project”. Heisenberg’s research was important to the war effort and he soon became a leading figure in the war-time fission research. Germany did not succeed in building an atomic bomb during the war. Did Heisenberg actively delay the development of a nuclear weapon or did he lack the scientific competence? Were technical problems the crucial stumbling-block or financial cuts on the part of the German army command? Heisenberg’s role is still disputed today. After the war and one year of internment in England, Heisenberg put much time and energy into rebuilding the scientific landscape in West Germany, both in the field of physics and in reestablishing international contacts. Those were interests that linked him with the ideas of the Lindau Nobel Laureate Meetings. In his own scientific work beginning in the 1950s Heisenberg focused on the search for a unified quantum theory of physics, sometimes called the World Formula, but this proved to be a scientific dead end. His institutional and public activities grew in importance. He supported nuclear research for civilian purposes but strongly opposed its military use. He underscored that view in Lindau, where he signed the Mainau Declaration in 1955. In a time overshadowed by the Cold War and the threat of nuclear warfare the Nobel laureates took a clear position: On July 15, 1955 18 Nobel Prize winners signed the declaration, among them Max Born, Werner Heisenberg and Otto Hahn. Within a year they were joined by 34 more Nobel Prize winners. Heisenberg and other scientists also used the stage in Lindau for other discussions. The meetings were ideal for the planning of large international projects. There is one feature that marked the Lindau dialogue from the start. Its orientation towards the future. Lindau has been an ideal forum to raise new ideas. Here for example Werner Heisenberg initiated the process leading to the establishment of CERN. In Lindau visions of the future in science and research have always been discussed Heisenberg not only acted behind the scenes but also enjoyed giving lectures about future international projects. On 1 February 1976, three years after his last visit to Lake Constance, Werner Heisenberg died of cancer at the age of 74. The beauty of nature, as revealed to Heisenberg in the mathematical world of the smallest particles, fascinated him all his life. The principles of the quantum mechanics he founded continue to fascinate us today.