Bohr received his doctorate in 1911. Working with Ernest Rutherford at his laboratory in Manchester in 1912 he began developing models of the atom in which electrons were based in rings around the nucleus. He returned to Copenhagen later that year to lecture at the university and in 1920 was appointed director of the Institute of Theoretical Physics, a position he held until his death.
It was in Copenhagen that he developed his theory of atomic structure by applying quantum theory to the observations of radiation emitted by atoms. For this, he was awarded the Nobel Prize for Physics in 1922.
In 1940, during the German occupation of Denmark, Bohr took an active part in the resistance movement. In 1943 he escaped from Denmark with his family, eventually making it to the United States. It was here that he became involved in the development of the atomic bomb, helping to explain the process of nuclear fission. In 1952 he played an important part in creating the European Centre for Nuclear Research (CERN).