The station serves as a base for the exploration of the Gamma Quadrant via the Bajoran wormhole, and is a hub of trade and travel for the sector's denizens. It is run by a joint crew of Starfleet and Bajoran officers, and it is the home port of a number of Starfleet runabouts and the USS Defiant. The station and its crew play a vital role to the events surrounding the Bajoran sector, the wormhole, and the Dominion War.
The promenade is the main public thoroughfare in which visitors and residents congregate, on which can be found Quark's Bar (the crew's most frequently-seen off-hours location), the infirmary, the replimat, a Bajoran temple, Garak's clothing shop, chief of security Odo's office, a Klingon restaurant, a mineral assay office, a candy kiosk, and, for a brief time during the first season, Keiko O'Brien's classroom. There are normally about 300 permanent residents of the station, though the station can accommodate up to 7,000.
Originally a Cardassian mining and refinery station named "Terok Nor" in orbit around Bajor, it was built by slave Bajoran labor under Cardassian rule in 2351. The station was commanded by Gul Dukat, the last Cardassian prefect of Bajor. It was abandoned toward the end of the Cardassian occupation of Bajor in 2369; the Cardassians removed anything of value on their way out.
In 2369, the Bajorans assumed control of the station. The Bajoran provisional government requested the assistance of the United Federation of Planets, who renamed it Deep Space Nine (DS9) and placed Commander Benjamin Sisko in command. Despite the Federation presence, the station remains subject to Bajoran law. Shortly after Sisko assumes command, his crew discovers the Bajoran wormhole. The station is moved to the mouth of the wormhole to secure Bajor's claim to it, after which the station assumes great commercial, scientific and strategic importance.
After the encounter with the Dominion in 2370 in which the Galaxy class USS Odyssey was destroyed by just three Dominion vessels and owing to other threats, it became obvious that the station's existing occupation-era weapons would be insufficient in defending the station. Utilising surplus and recycled parts along with some new parts, the station's weapons and defensive systems were upgraded. The upgrade included the installation of multiple rotary torpedo launchers on the docking pylons and weapons sail towers, stowable phaser banks that stow into former runabout maintenance bays when not in use and improved shields that extend 300 meters around the station. The total capacity of torpedoes was increased to 5000.
These upgrades were first used against the Klingons in their offensive against Cardassia in early 2372. At the beginning of the Dominion War in late 2373, the station was temporarily lost to the Dominion. In early 2374, Federation and Klingon forces retook it after the Battle of Bajor.
Aside from a failed Bajoran military coup, the Dominion's occupation, and a brief leave of absence from late 2374 to early 2375, Sisko, promoted to captain in 2371, remained in command of Deep Space Nine. In late 2375, at the end of the Dominion War, Colonel Kira Nerys assumed command.
In 2372, the Terran Rebellion wrests control of the station away from the Alliance. The Alliance, determined to recapture the station, sends a fleet under Regent Worf to fight the rebels. The rebels are able to build their own Defiant based on schematics for the Defiant in the primary universe, and they use it to defeat the Alliance fleet. Terok Nor remains a base of operations for the Terran Rebellion for at least the next three years.