Theodor Kaluza (1885-1945), German mathematician & theoretical physicist. In 1921, with Einstein's help, he published a paper - On the unity problem of physics - which attempted to unify Einstein's theory of gravity and Maxwell's theory of electromagnetism. He achieved this by introducing a fifth dimension which is 'compactified' so that it is imperceptibly small. The work was based on what is now known as the Kaluza-Klein field theory, which involved field equations in five- dimensional space that he had developed together with the mathematician Oskar Klein (1894-1977).