  We explore various tree-level double copy constructions for amplitudes
including massive particles with spin. By working in general dimensions, we use
that particles with spins $s\leq 2$ are fundamental to argue that the
corresponding double copy relations partially follow from compactification of
their massless counterparts. This massless origin fixes the coupling of gluons,
dilatons and axions to matter in a characteristic way (for instance fixing the
gyromagnetic ratio), whereas the graviton couples universally reflecting the
equivalence principle. For spin-1 matter we conjecture all-order Lagrangians
reproducing the interactions with up to two massive lines and we test them in a
classical setup, where the massive lines represent spinning compact objects
such as black holes. We also test the amplitudes via CHY formulae for both
bosonic and fermionic integrands. At five points, we show that by applying
generalized gauge transformations one can obtain a smooth transition from
quantum to classical BCJ double copy relations for radiation, thereby providing
a QFT derivation for the latter. As an application, we show how the theory
arising in the classical double copy of Goldberger and Ridgway can be naturally
identified with a certain compactification of $\mathcal{N}=4$ Supergravity.
