  CO observations of 0<z<4 radio galaxies are presented. The L_CO upper limits
for the high-redshift powerful radio galaxies (HzPRGs: z > 1, P_408MHz > 10^27
Watts/Hz) are consistent with no evolution in molecular gas (H_2) mass with
redshift and/or radio power. Of the low-redshift powerful radio galaxies
(LzPRGs: z<0.2, P_408MHz MHz > 10^23.5 W/Hz) observed, only one F-R II galaxy
has been detected in CO, whereas approximately 50% of the radio-compact (FC)
and F-R I galaxies have been detected. The CO and imaging data to date imply
that either F-R II galaxies result from mergers of gas-poor galaxies relative
to FC/F-R I galaxies, or that some FC/F-R I galaxies evolve into F-R II
galaxies. In either scenario, the radio activity in powerful radio galaxies is
most likely triggered by a merger event, and H_2 may be the fuel for the active
galactic nucleus (AGN) in the early stages of the merger.
