  The discrete time crystal (DTC) is a recently discovered phase of matter that
spontaneously breaks time-translation symmetry. Disorder-induced
many-body-localization is required to stabilize a DTC to arbitrary times, yet
an experimental investigation of this localized regime has proven elusive.
Here, we observe the hallmark signatures of a many-body-localized DTC using a
novel quantum simulation platform based on individually controllable $^{13}$C
nuclear spins in diamond. We demonstrate the characteristic long-lived
spatiotemporal order and confirm that it is robust for generic initial states.
Our results are consistent with the realization of an out-of-equilibrium
Floquet phase of matter and establish a programmable quantum simulator based on
solid-state spins for exploring many-body physics.
