  The high redshift sub-mm sources discovered by SCUBA are widely believed to
represent the dust-enshrouded formation of massive elliptical galaxies. Given
the strong evidence for a link between the formation of the spheroid and the
growth of the central black hole, one might expect to see a luminous quasar at
the nucleus of every SCUBA source. Somewhat surprisingly, however, only a very
small fraction (~5%) are detected by Chandra with quasar luminosities. In this
paper I discuss some of the implications of these results and discuss the
accumulating evidence that sub-mm sources and quasars may represent different
stages in the evolutionary sequence of a massive proto-spheroid.
