  It is commonly accepted that radio-loud active galactic nuclei are hosted
exclusively by giant elliptical galaxies. We analyze high-resolution optical
Hubble Space Telescope images of a sample of radio galaxies with extended
double-lobed structures associated with disk-like optical counterparts. After
systematically evaluating the probability of chance alignment between the radio
lobes and the optical counterparts, we obtain a sample of 18 objects likely to
have genuine associations. The host galaxies have unambiguous late-type
morphologies, including spiral arms, large-scale dust lanes among the edge-on
systems, and exceptionally weak bulges, as judged by the low global
concentrations, small global S\'{e}rsic indices, and low bulge-to-total light
ratios (median $B/T = 0.13$). With a median S\'{e}rsic index of 1.4 and low
effective surface brightnesses, the bulges are consistent with being pseudo
bulges. The majority of the hosts have unusually large stellar masses (median
$M_* = 1.3\times 10^{11}\, M_\odot$) and red optical colors (median $g-r =
0.69\,$mag), consistent with massive, quiescent galaxies on the red sequence.
We suggest that black hole mass (stellar mass) plays a fundamental role in
launching large-scale radio jets, and that the rarity of extended radio lobes
in late-type galaxies is the consequence of the steep stellar mass function at
the high-mass end. The disk radio galaxies have mostly Fanaroff-Riley type II
morphologies yet lower radio power than sources of a similar type traditionally
hosted by ellipticals. The radio jets show no preferential alignment with the
minor axis of the galactic bulge or disk, apart from a possible mild tendency
for alignment among the most disk-dominated systems.
