  We have studied the host galaxies of a sample of radio-loud AGN spanning more
than four decades in the energy output of the nucleus. The core sample includes
40 low-power sources (BL Lac objects) and 22 high-power sources (radio-loud
quasars) spanning the redshift range z~0.15 to z~0.5, all imaged with the high
spatial resolution of HST. All of the sources are found to lie in luminous
elliptical galaxies, which follow the Kormendy relation for normal ellipticals.
A very shallow trend is detected between nuclear brightness (corrected for
beaming) and host galaxy luminosity. Black hole masses are estimated for the
entire sample, using both the bulge luminosity--black hole mass and the
velocity dispersion--black hole mass relations for local galaxies. The latter
involves a new method, using the host galaxy morphological parameters, mu_e and
r_e, to infer the velocity dispersion, sigma, via the fundamental plane
correlation. Both methods indicate that the entire sample of radio-loud AGN are
powered by very massive central black holes, with M_{black hole} ~ 10^8 to
10^10 M_{sun}$. Eddington ratios range from L/L_{Eddington} ~ 2 x 10^-4 to ~1,
with the high- power sources having higher Eddington ratios than the low-power
sources. Overall, radio-loud AGN appear to span a very large range in accretion
efficiency, which is all but independent of the mass of the host galaxy.
