"The Sword of Kahless" is the 81st episode of the American science fiction television series Star Trek: Deep Space Nine, the ninth of the fourth season. It originally aired on November 20, 1995, in broadcast syndication. The story was created by Richard Danus and was turned into a teleplay by Hans Beimler. The episode was directed by Star Trek: The Next Generation alumnus LeVar Burton, and featured the return of John Colicos as Kor. Colicos had first appeared as Kor in the Star Trek: The Original Series episode "Errand of Mercy", and had previously appeared in this series in the episode "Blood Oath".

Set in the 24th century, the series follows the adventures on Deep Space Nine, a space station located near a stable wormhole between the Alpha and Gamma quadrants of the Milky Way Galaxy. In this episode, Kor returns to the station to recruit Lt. Cmdr. Worf (Michael Dorn) and Lt. Cmdr. Jadzia Dax (Terry Farrell) to help to find the ancient Sword of Kahless, the legendary founder of the Klingon Empire. After they find the sword, they are forced to evade the forces of Toral (Rick Pasqualone), son of Duras, and Worf and Kor come to blows over the future use of the weapon.

After the character Worf, who originated on Star Trek: The Next Generation, joined the cast of Deep Space Nine at the beginning of the fourth season, this was the first episode to feature Worf as a main character in its central storyline. Due to time restraints in filming, there were edits made to the scripts and the production team were forced to make best use of the cave sets which had been seen on the show previously.