Leopold Kronecker. Portrait of Leopold Kronecker (1823-91), German mathematician. After graduating from Berlin University, Kronecker spent 10 years managing his family business. When he returned to Berlin he was financially independent and lectured only for his own pleasure. He investigated complex units, and his work on number theory, algebra and elliptic functions unified much previous research. He believed that mathematics should be based only on whole numbers (integers) & developed a system of axioms to support his views. In linear algebra he developed the Kronecker delta and established its use in evaluating determinants; this was the first time a tensor quantity had been used.