What was the name of Niels Bohr's brother, a famous mathematician?

Niels Bohr’s brother, the famous mathematician Harald Bohr, helped establish the field of almost periodic functions.

Harald August Bohr was born in Copenhagen on 22 April 1887, two years after Niels. He studied mathematics at the University of Copenhagen, earned his master’s degree in 1909, and received his doctorate in 1910. His mathematical work focused especially on analysis, number theory, Dirichlet series, and almost periodic functions.

Harald was also an accomplished footballer. He played for Akademisk Boldklub alongside Niels, who usually played as a goalkeeper while Harald played in defence. Harald represented Denmark at the 1908 Olympic football tournament in London, where the team won a silver medal.

A common mix-up is Aage Bohr, who was Niels’s son rather than his brother. Aage later became a physicist and won the 1975 Nobel Prize in Physics. Christian Bohr was Niels and Harald’s father, a distinguished physiologist, not Harald’s brother.