POPULATION: Unknown, likely millions
Gao is a human outer colony world with a strong national identity and ties to insurrectionists. Prior to the Human-Covenant War, Gao was allied with the insurrection, though is loosely governed by the UEG following the end of the war. Gao maintains ties with Venezia, another outer colony with powerful connections to the insurrection.
Following the end of the war, Gao was the focus of the UNSC Marine Corps 717th Xeno-Materials Exploitation Battalion due to the discovery of a potential Forerunner ancilla buried within a cave system on the planet. During the 717th’s time on Gao’s surface, the government on Gao experienced a coup, and power transitioned to the much more UNSC-hostile Arlo Casille. The UNSC was forced to retreat off the planet under fire from the local military, though they successfully extracted the Forerunner ancilla from Gao.