The master two-loop diagram with masses

In every mass case needed for QCD and QED two-point functions, the most difficult two-loop scalar Feynman diagram is reduced, by a systematic dispersive method, to a single integral of logarithms, whose expansion is obtained for large and, when appropriate, small momenta. The new results for the case with an intermediate state comprising three massive particles are needed for the two-loop calculation of fermion propagators.