Extreme dyonic black holes in string theory

Supersymmetric extreme dyonic black holes of toroidally compactified heterotic or type II string theory can be viewed as lower-dimensional images of solitonic strings wound around a compact dimension. We consider conformal sigma models which describe string configurations corresponding to various extreme dyonic black holes in four and five dimensions. These conformal models have regular short-distance region equivalent to a WZW theory with level proportional to magnetic charges. Arguments are presented suggesting a universal relation between the black hole entropy (area) and the statistical entropy of BPS-saturated oscillation states of solitonic string.[Extended version of a talk at the Workshop "Frontiers in Quantum Field Theory", in honor of the 60th birthday of K. Kikkawa (Osaka, Japan, 14-17 December 1995)]