  Since their initial discovery, the origin of isolated white dwarfs (WDs) with
magnetic fields in excess of $\sim$1 MG has remained a mystery. Recently, the
formation of these high-field magnetic WDs has been observationally linked to
strong binary interactions incurred during post-main-sequence evolution.
Planetary, brown dwarf or stellar companions located within a few AU of
main-sequence stars may become engulfed during the primary's expansion off the
main sequence. Sufficiently low-mass companions in-spiral inside a common
envelope until they are tidally shredded near the natal white dwarf. Formation
of an accretion disk from the disrupted companion provides a source of
turbulence and shear which act to amplify magnetic fields and transport them to
the WD surface. We show that these disk-generated fields explain the observed
range of magnetic field strengths for isolated, high-field magnetic WDs.
Additionally, we discuss a high-mass binary analogue which generates a
strongly-magnetized WD core inside a pre-collapse, massive star. Subsequent
core-collapse to a neutron star may produce a magnetar.
