Keiko O'Brien is a character in the fictional Star Trek universe, played by actress Rosalind Chao. Introduced in 1991, she is the civilian spouse of Starfleet crew member Miles O'Brien appearing occasionally in later seasons of the series Star Trek: The Next Generation (1987–1994), and more frequently as a supporting character throughout Star Trek: Deep Space Nine (1993–1999), as well as in related media such as novels. The producers wanted her as a regular character on Deep Space Nine, but Chao was only available part-time.

Deep Space Nine is a fictional space station, the eponymous primary setting of the American science fiction television series Star Trek: Deep Space Nine which aired from 1993 to 1999. It 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, as well as the starship USS Defiant.