  Using Subaru/Suprime-Cam wide-field imaging and both Keck/ESI and LBT/MODS
spectroscopy, we identify and characterize a compact star cluster, which we
term NGC 3628-UCD1, embedded in a stellar stream around the spiral galaxy NGC
3628. The size and luminosity of UCD1 are similar to $\omega$ Cen, the most
luminous Milky Way globular cluster, which has long been suspected to be the
stripped remnant of an accreted dwarf galaxy. The object has a magnitude of
$i=19.3$ mag (${\rm L}_{\rm i}=1.4\times10^{6}~{\rm L}_{\odot}$). UCD1 is
marginally resolved in our ground-based imaging, with a half-light radius of
$\sim10$ pc. We measure an integrated brightness for the stellar stream of
$i=13.1$ mag, with $(g-i)=1.0$. This would correspond to an accreted dwarf
galaxy with an approximate luminosity of ${\rm L}_i\sim4.1\times10^{8}~{\rm
L}_{\odot}$. Spectral analysis reveals that UCD1 has an age of $6.6$ Gyr ,
$[\rm{Z}/\rm{H}]=-0.75$, an $[{\alpha}/\rm{Fe}]=-0.10$. We propose that UCD1 is
an example of an $\omega$ Cen-like star cluster possibly forming from the
nucleus of an infalling dwarf galaxy, demonstrating that at least some of the
massive star cluster population may be created through tidal stripping.
