Built in 2351, the Deep Space Nine (a.k.a. DS9) was originally used for mining operations run by the Cardassian Empire after they conquered the Bajoran people. When the Cardassians occupying forces relinquished their claim to the station and retreated the system in 2359, the Federation took control of DS9 at the request of the Bajorans and appointed Starfleet officer Benjamin Sisko (Avery Brooks) as the station's new commander.

His support staff included:

• Major Kira Nerys (Nana Visitor), a Bajoran liaison officer
• Commander Odo (Rene Auberjonois), a shape-shifting Security Chief
• Chief of Operations Officer Miles O'Brien (Colm Meaney)
• Head Physician Julian Bashir (Siddig El Fadil)
• Trill Chief Science Officer Jadzia "Old Man" Dax (Terry Farrell) whose body was inhabited by a 300-year-old symbiont being.

Among the other occupants aboard the DS9 were:

• Quark, the fanged Ferengi proprietor of Quark's Bar
• Quark's brother Rom (Max Grodenchick) and his son Nog (Aron Eisenberg)
• Garak, a Cardassian spy turned tailor who ran a clothing shop on the station's Promenade
• Keiko, Miles O'Brien's botanist teacher wife; their daughter Molly (Hana Hatae)
• Jake Sisko (Cirroc Lofton), the son of Commander Sisko.

Before the Federation occupation of the station, DS9 was called "Terok Nor" by the Cardassians. DS9 held approximately 300 personnel and visitors. Its shape resembled a ring within a ring with three equally spaced hooked towers protruding from the top and bottom of the outer circle.

The DS9 station was later retaken by the Cardassians who joined forces with The Dominion (a.k.a. "The Founders"), a shape-shifting race of aliens from the Gamma Quadrant. But, the station was again reclaimed by the Federation. See also Captain Sisko's Baseball