  We prove global Schauder estimates for kinetic Kolmogorov equations with
coefficients that are H\"older continuous in the spatial variables but only
measurable in time. Compared to other available results in the literature, our
estimates are optimal in the sense that the inherent H\"older spaces are the
strongest possible under the given assumptions: in particular, under a
parabolic H\"ormander condition, we introduce H\"older norms defined in terms
of the intrinsic geometry that the operator induces on the space-time
variables. The technique is based on the existence and the regularity estimates
of the fundamental solution of the equation. These results are essential for
studying backward Kolmogorov equations associated with kinetic-type diffusions,
e.g. stochastic Langevin equation.
