  We have compelling evidence for stellar-mass black holes (BHs) of ~5-80 M_sun
that form through the death of massive stars. We also have compelling evidence
for so-called supermassive BHs (10^5-10^10 M_sun) that are predominantly found
in the centers of galaxies. We have very good reason to believe there must be
BHs with masses in the gap between these ranges: the first ~10^9 M_sun BHs are
observed only hundreds of millions of years after the Big Bang, and all
theoretically viable paths to making supermassive BHs require a stage of
"intermediate" mass. However, no BHs have yet been reliably detected in the
100-10}^5 M_sun mass range. Uncovering these intermediate-mass BHs of 10^3-10^5
M_sun is within reach in the coming decade. In this white paper we highlight
the crucial role that 30-m class telescopes will play in dynamically detecting
intermediate-mass black holes, should they exist.
