His idea that fundamental forces can be unified by introducing additional dimensions was reused much later for string theory.
Kaluza was born to a Roman Catholic family from the town of Ratibor (present-day Racibórz in Poland) in the German Empire's Prussian Province of Silesia.
Perhaps his finest mathematical work is the textbook Höhere Mathematik für den Praktiker, which was written jointly with Georg Joos.
He refused the Nazi ideology, and his appointment to the Göttingen professorship was possible only with difficulties and by assistance of his colleague Helmut Hasse.
Strange stories were told of his private life, for example, that he taught himself to swim during his thirties by reading a book about it and succeeded at his first attempt in the water.