Niels Henrik David Bohr (October 7 1885 - November 18 1962) was a Danish physicist. He made essential contributions to understanding atom structure and quantum mechanics. He was born (and died) in Copenhagen, Denmark.
Bohr got his doctorate at Copenhagen University in 1911. He then studied under Ernest Rutherford in Manchester, England. Based on Rutherford's theories, Bohr published his Bohr model about atom structure in 1913, introducing the theory of electrons travelling on orbits around the atom's nucleus, with the outer orbits holding more electrons than the inner ones, thereby determining the chemical properties of the atom. Also, an electron could drop from an outer orbit to an inner one, emitting a photon (light) of discrete energy. This became the basis for quantum theory.
In 1916, Bohr became professor at the University of Copenhagen, and director of the newly constructed "Institute of Theoretical Physics" in 1920. In 1922, he was awarded the Nobel Prize in physics for developing the Copenhagen interpretation of quantum mechanics.
One of Bohr's most famous students was Werner Heisenberg. There is a play which ran on Broadway for a time, written by Michael Frayn, about what might have happened between the student and pupil when Heisenberg was the head of the German atomic bomb project and he went to his former teacher to pick his brain about the subject.
During World War II, he went to Copenhagen, then to Los Alamos, New Mexico, USA, to help with the construction of the atomic bomb. After the war, he returned to Copenhagen, advocating for a peaceful use of atomic energy.