NASA's Mars Science Laboratory mission, with its Curiosity rover, has been exploring Gale crater since 2012 with the goal of assessing its potential to support life. The mission has compiled compelling evidence that the crater basin accumulated sediment transported by marginal rivers into lakes that likely persisted for millions of years in the early Hesperian. Fluids simultaneously circulated in the subsurface and likely existed through the dry phases of lake bed exposure and eolian deposition creating a continuously habitable deep biosphere environment that persisted of millions to even hundreds of millions of years, conceivably even into early Amazonian time. Geochemical and mineralogical assessments indicate that ancient environmental conditions would have been suitable for sustaining life, if it ever were present. A diversity of organic molecules has been preserved, though degraded, with evidence for more complex precursors. In situ studies of modern wind-driven sediment transport and multiple large and active aeolian deposits have led to advances in physical theory of boundary conditions and bedform development. Despite 9 years of exploration, rover systems and science instruments remain healthy and capable of performing all key scientific objectives.