  We report the discovery of RG1M0150, a massive, recently quenched galaxy at
z=2.636 that is multiply imaged by the cluster MACSJ0150.3-1005. We derive a
stellar mass of log M_*=11.49+0.10-0.16 and a half-light radius of R_e,maj
=1.8+-0.4 kpc. Taking advantage of the lensing magnification, we are able to
spatially resolve a remarkably massive yet compact quiescent galaxy at z>2 in
ground-based near-infrared spectroscopic observations using Magellan/FIRE and
Keck/MOSFIRE. We find no gradient in the strength of the Balmer absorption
lines over 0.6 R_e - 1.6 R_e, which are consistent with an age of 760 Myr. Gas
emission in [NII] broadly traces the spatial distribution of the stars and is
coupled with weak Halpha emission (log [NII]/Halpha = 0.6+-0.2), indicating
that OB stars are not the primary ionizing source. The velocity dispersion
within the effective radius is sigma_e = 271+-41 km/s. We detect rotation in
the stellar absorption lines for the first time beyond z~1. Using a
two-integral Jeans model that accounts for observational effects, we measure a
dynamical mass of log M_dyn =11.24+-0.14 and V/sigma=0.70+-0.21. This is a high
degree of rotation considering the modest observed ellipticity of 0.12+-0.08,
but it is consistent with predictions from dissipational merger simulations
that produce compact remnants. The mass of RG1M0150 implies that it is likely
to become a slowly rotating elliptical. If it is typical, this suggests that
the progenitors of massive ellipticals retain significant net angular momentum
after quenching which later declines, perhaps through accretion of satellites.
