  We present confirmation of the cluster MOO J1142+1527, a massive galaxy
cluster discovered as part of the Massive and Distant Clusters of WISE Survey.
The cluster is confirmed to lie at $z=1.19$, and using the Combined Array for
Research in Millimeter-wave Astronomy we robustly detect the Sunyaev-Zel'dovich
(SZ) decrement at 13.2$\sigma$. The SZ data imply a mass of
$\mathrm{M}_{200m}=(1.1\pm0.2)\times10^{15}$ $\mathrm{M}_\odot$, making MOO
J1142+1527 the most massive galaxy cluster known at $z>1.15$ and the second
most massive cluster known at $z>1$. For a standard $\Lambda$CDM cosmology it
is further expected to be one of the $\sim 5$ most massive clusters expected to
exist at $z\ge1.19$ over the entire sky. Our ongoing Spitzer program targeting
$\sim1750$ additional candidate clusters will identify comparably rich galaxy
clusters over the full extragalactic sky.
