  We use redshift observations of two deep 1.4GHz fields to probe the evolution
of the bright end of the radio galaxy luminosity function to z=1.5. We show
that the number of galaxies with radio power that would correspond locally to
an ultraluminous infrared galaxy (ULIG) evolves rapidly over this redshift
range. The optical spectra and X-ray luminosities are used to refine this
result by separating the sources with clear active galactic nucleus (AGN)
signatures from those that may be dominated by star formation. Both populations
show extremely rapid evolution over this redshift range. We find that the
number of sources with ULIG radio power and no clear AGN signatures evolves as
(1+z)^(7).
