Niels Henrik David Bohr (Danish: ; 7 October 1885 -18 November 1962) was a Danish physicist, philosopher and footballer, who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. One of his sons, Aage Bohr, was also a physicist and in 1975 also received the Nobel Prize. Bohr was a passionate footballer who played goalkeeper for the Copenhagen-based Akademisk Boldklub, but was not as accomplished a player as his brother Harald Bohr, who played for the Danish national team at the 1908 Summer Olympics.
Bohr developed the Bohr model of the atom with the atomic nucleus at the centre and electrons in orbit around it, which he compared to the planets orbiting the Sun. He worked on the idea in quantum mechanics that electrons move from one energy level to another in discrete steps, not continuously. He founded the Institute of Theoretical Physics at the University of Copenhagen, now known as the Niels Bohr Institute, which opened in 1920. Bohr mentored and collaborated with physicists including Hans Kramers, Oskar Klein, George de Hevesy and Werner Heisenberg. He predicted the existence of a new zirconium-like element, which was named hafnium, after Copenhagen, when it was discovered. Later, the element Bohrium was named after him. He conceived the principle of complementarity: that items could be separately analysed as having contradictory properties, like behaving as a wave or a stream of particles. The notion of complementarity dominated his thinking on both science and philosophy.
During the 1930s, Bohr gave refugees from Nazism temporary jobs at the Institute, provided them with financial support, arranged for them to be awarded fellowships from the Rockefeller Foundation, and ultimately found them places at various institutions around the world. After Denmark was occupied by the Germans, he had a dramatic meeting with Heisenberg, the head of the German nuclear energy project in Copenhagen. In 1943, fearing arrest, Bohr fled to Sweden, where he persuaded King Gustav V of Sweden to make public Sweden's willingness to provide asylum. He was then flown to Britain, where he joined the British Tube Alloys nuclear weapons project, and was part of the British team of physicists who worked on the Manhattan Project.
After the war, Bohr called for international cooperation on nuclear energy. He was involved with the establishment of CERN, and became the first chairman of the Nordic Institute for Theoretical Physics in 1957. He was also involved with the founding of the Ris DTU National Laboratory for Sustainable Energy.