Niels Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory. He developed the Bohr model of the atom, which proposed that electrons orbit the nucleus in discrete energy levels and can jump between these levels. Bohr founded the Niels Bohr Institute in Copenhagen, where he mentored and collaborated with other prominent physicists. He was influenced by the existentialist philosopher Søren Kierkegaard, though he disagreed with some aspects of Kierkegaard's Christian philosophy due to Bohr's atheism.