  The recent discovery of a neutron star accretor in the ultra-luminous X-ray
source M82 X-2 challenges our understanding of high-mass X-ray binary formation
and evolution. By combining binary population synthesis and detailed
mass-transfer models, however, we show that the binary parameters of M82 X-2
are not surprising provided non-conservative mass transfer is allowed.
Specifically, the donor-mass lower limit and orbital period measured for M82
X-2 lie near the most probable values predicted by population synthesis models,
and systems such as M82 X-2 should exist in approximately 13% of the galaxies
with a star-formation history similar to M82. We conclude that the binary
system that formed M82 X-2 is most likely less than 50 Myr old and contains a
donor star which had an initial mass of approximately 8-10 M$_\odot$, while the
NS's progenitor star had an initial mass in the $8-25\,\rm M_{\odot}$ range.
The donor star still currently resides on the main sequence, and is capable of
continued MT on the thermal timescale, while in the ultra-luminous X-ray
regime, for as long as 400,000 years.
