A former Cardassian ore processing station orbiting Bajor and next to the Bajoran wormhole.
Deep Space Nine began as Terok Nor, a Cardassian ore-processing station in orbit of Bajor, built during the Cardassian occupation of that world. It was a three-ring station with a distinctive pylons-and-docking-ring design, and it was home to many Bajoran forced labourers. When the Cardassians withdrew, the station was handed to the Bajoran provisional government and placed under Federation administration.
Commander Benjamin Sisko took command and the station became a hub of trade, diplomacy and intrigue. Its crew included Major Kira Nerys, the Bajoran liaison, Odo the security chief, Dr. Julian Bashir, Chief Miles O'Brien, Jadzia Dax, and the Ferengi bartender Quark. The discovery of a stable wormhole near Bajor opened the Gamma Quadrant, raising the station to strategic importance and bringing the Bajoran faith's Prophets into the story.
Deep Space Nine became a front line when the Dominion arrived. It was held by Starfleet, taken over by the Cardassians and Dominion for a time, and then recaptured. It endured sieges and sabotage but remained a symbol of resilience. After the war ended, the station continued as a Federation-Bajoran facility and a centre of rebuilding.