  The recent development of unified theories of active galactic nuclei (AGN)
has indicated that there are two physically distinct classes of these objects -
radio-loud and radio-quiet. The primary observational distinctions between the
two types are: (1) The radio-loud objects produce large scale radio jets and
lobes, with the kinetic power of the jets being a significant fraction of the
total bolometric luminosity. On the other hand, the weak radio ejecta of the
radio-quiet objects are energetically insignificant. (2) The radio-loud objects
are associated with elliptical galaxies which have undergone recent mergers,
while the radio-quiets prefer spiral hosts. (3) The space density of the
radio-louds at a given optical luminosity is $\approx$ 10 times lower than that
of the radio-quiets. Despite these differences, the (probably) thermal
emissions from the AGN (continua and lines from X-ray to infrared wavelengths)
are quite similar in the two classes of object. We argue that this last result
suggests that the black hole masses and mass accretion rates in the two classes
are not greatly different, and that the difference between the classes is
associated with the spin of the black hole.
  We assume that the normal process of accretion through a disk does not lead
to rapidly spinning holes, and propose instead that galaxies (e.g. spirals)
which have not suffered a recent major merger event contain non-rotating or
only slowly rotating black holes. When two such galaxies merge, the two black
holes are known to form a binary and we assume that they eventually coalesce.
In the small fraction of mergers in which the two ``parent'' galaxies contain
very massive holes of roughly equal mass, a rapidly spinning, very massive hole
results. It is proposed that such mergers are the progenitors of powerful radio
