  Benchmark brown dwarf companions with well-determined ages and
model-independent masses are powerful tools to test substellar evolutionary
models and probe the formation of giant planets and brown dwarfs. Here, we
report the independent discovery of HIP~21152~B, the first imaged brown dwarf
companion in the Hyades, and conduct a comprehensive orbital and atmospheric
characterization of the system. HIP~21152 was targeted in an ongoing
high-contrast imaging campaign of stars exhibiting proper motion changes
between Hipparcos and Gaia, and was also recently identified by Bonavita et al.
(2022) and Kuzuhara et al. (2022). Our Keck/NIRC2 and SCExAO/CHARIS imaging of
HIP~21152 revealed a comoving companion at a separation of
$0.37^{\prime\prime}$ (16 au). We perform a joint orbit fit of all available
relative astrometry and radial velocities together with the Hipparcos-Gaia
proper motions, yielding a dynamical mass of $24^{+6}_{-4}\,\mathrm{M_{Jup}}$,
which is $1{-}2{\sigma}$ lower than evolutionary model predictions. Hybrid
grids that include the evolution of cloud properties best reproduce the
dynamical mass. We also identify a comoving wide-separation
($1837^{\prime\prime}$ or $7.9 \times 10^4 \, \mathrm{au}$) early-L dwarf with
an inferred mass near the hydrogen-burning limit. Finally, we analyze the
spectra and photometry of HIP~21152~B using the Saumon & Marley (2008)
atmospheric models and a suite of retrievals. The best-fit grid-based models
have $f_{\mathrm{sed}}=2$, indicating the presence of clouds,
$T_{\mathrm{eff}}=1400 \, \mathrm{K}$, and $\log{g}=4.5 \, \mathrm{dex}$. These
results are consistent with the object's spectral type of $\mathrm{T0\pm1}$. As
the first benchmark brown dwarf companion in the Hyades, HIP~21152~B joins the
small but growing number of substellar companions with well-determined ages and
dynamical masses.
