Gao

Gao, known to the Forerunners as Edod, is a remote human Outer Colony in the Cordoba system that survived the Human-Covenant War. While nominally under the administration of the Unified Earth Government, both the people and the colonial government of Gao maintain a strong sense of national identity and anti-UEG sentiments are commonplace. The planet's Montero region was home to a vast cavern system — in fact an artificial Forerunner construct designed to support the Maginot Line.

History
During the Insurrection, Gao openly supported the Insurrectionists. Following the Human-Covenant War, Gao remained highly independence-minded and sought to strengthen its ties with nearby colonies, such as Venezia, rather than the UEG.

In May 2553, the UNSC's 717th Xeno-Materials Exploitation Battalion protected by Blue Team arrived at the planet to recover a Forerunner ancilla in the Montero Cave System. The UNSC subsequently declared the cave system off-limits to outsiders, but civilians continued to sneak into the caves anyway in search of rumored miracle cures; soon after, an increasing number of these civilians were found brutally murdered. With tensions heightening between Gao's government and the UNSC, Special Inspector Veta Lopis of the Gao Ministry of Protection was assigned with investigating the serial killer on July 2, 2553. Meanwhile, the Insurrectionist-minded Gao politician Arlo Casille allied with the ex-Covenant faction known as the Keepers of the One Freedom to prevent the UNSC from gaining control of the Forerunner technology in the caves. Seeking to drive out the UNSC forces without forcing Gao itself into a war, Casille smuggled the Keepers on the planet, where they attacked the UNSC research battalion, resulting in several days of fighting in the Montero region. In the end, the UNSC forces evacuated from the planet with the Forerunner AI, Intrepid Eye, while destroying the Montero Cave System with a HAVOK tactical nuclear weapon.

Topography
Gao is a lush, jungled planet; viewed from space, the planet is largely mottled green fading to gray at both poles, which are covered by large deserts. Gao's jungles and caverns support a rich ecology with numerous native species (including saurios, frilled salamanders, idjoms, jungaloons, ribbon-snakes, no-shell snails, speckled jungle dragons and glowfish), while the planet's polar barrens are inhabited by great gray apes.

Trivia
The planet may be named after a city of the same name in Mali.

List of appearances

 * Halo: Last Light
 * Halo 5: Guardians
 * Limited Edition
 * Halo Mythos: A Guide to the Story of Halo
 * Halo Fractures
 * Lessons Learned
 * A Necessary Truth