The strength and beauty of the Hungarian mathematical school is quite fascinating. Everybody knows Paul Erdős, but many mathematicians ignore that great minds such as Eugene Wigner and John von Neumann were actually Hungarian (schoolmates in Budapest and colleagues in Princeton). During the twentieth century, Budapest and Szeged were important cultural and scientific centers for Central and Eastern Europe, with influences from Germany and Russia. I maintain a list of Hungarian mathematicians. Comments are welcome!
Digression: the random matrices of Wigner and the operators algebras of von Neumann (beware that their works are not resctricted to these subjects!) were connected by the free probability theory of Voiculescu, a Romanian mathematician, in the late twentieth century.