Epoloch system

The  was a Forerunner-controlled system that is home to the Ur-Didact's first and greatest Shield World; Requiem.

Forerunner Era
Long before the Human-Forerunner war, the Warrior-Servant commander known as the Didact commissioned the construction of an artificial fortress world as his primary base of operations. The world was constructed in the Epoloch system. It is unknown if there were any battles in the system during the Human or Flood wars. As the Forerunner-Flood war drew to a close, the Greater Ark was destroyed by a net of Flood-controlled star roads, leaving only the secret Lesser Ark and Requiem as the last Forerunner bastions. While the Iso-Didact prepared to fire the Halo Array, the Ur-Didact returned to Epoloch where the last fleets of Warrior-Servants gathered. Bringing them into Requiem, the Ur-Didact used a Composer to digitize the consenting Prometheans, placing the compositions inside non-organic Sentinel armor. Before the destruction of Installation 12, the Ur-Didact also composed a population of humans. This caused the Librarian to be moved to uncharacteristic rage. She pursued the Ur-Didact to Epoloch and with the help of Endurance-of-Will, used a Light Rifle firing modified stun projectiles to incapacitate the Promethean. She then placed him in a Combat Cryptum and left for the Sol system as Requiem sealed shut behind her. The Epoloch System would go undisturbed for over 100,000 years. In 2554, the Storm Fleet arrived in-system with the intention of gaining entry to Requiem. They would be unsuccessful until 2557, when the wreck of the UNSC Forward Unto Dawn arrived in their midst. The presence of a Reclaimer caused the world to open.

Requiem Campaigns
After being dormant one hundred millennia, the Epoloch system bustled with Covenant reinforcements, the wreck of the UNSC Forward Unto Dawn, and Humanity's new flagship, the UNSC Infinity. The First Battle of Requiem commenced as the zealous Covenant swarmed into the newly opened Shield World in pursuit of one of their most powerful deities: the Didact. The UNSC Infinity arrived at Epoloch, following a set of coordinates found on Installation 03. The Infinity was grounded on the planet, where it encountered the bulk of the Storm Fleet and the Promethean constructs. Meanwhile the Ur-Didact was awoken inadvertently by the Master Chief and used the Combat Cryptum, his long-time prison, to wreak havoc on UNSC forces before leaving Requiem in his flagship, the Mantle's Approach. SPARTAN-117 followed in hot pursuit while the Infinity escaped the world and returned to Earth. Six months later the warship returned with a complement of ten frigates to retake Requiem. A vicious campaign ensued at high cost to both sides. The Covenant lost a staggering amount of their ground forces, although the Infinity's complement was completely annihilated during a space battle. Ultimately the Covenant would find what they sought: the ancilla of the Librarian, who presented two halves of the powerful Janus Key to Dr. Halsey. At this point Jul 'Mdama activated one of Requiem's fail-safes, slowly dragging the world into Epoloch, attempting to destroy the Infinity. The Infinity would narrowly avoid destruction, although Requiem was consumed in the overwhelming heat of the star. Its destruction triggered yet another fail-safe: the supernova of Epoloch itself. The star destabilized at an artificially enhanced speed and was destroyed.

Trivia

 * While Epoloch appears to be a blue B V-type star in Halo 3 and the Halo 4 Terminals, in the final cutscene of Shutdown and in Spartan Ops, it appears to be an orange K V-type star.