AKA The Kzinti Question
Larry Niven was contracted to write a story for the Star Trek Animated Series. Instead of being creative and writing something new, he took an older story "The Soft Weapon" from his Known Space series and rewrote it with Spock, Uhurua, and Sulu in place of the original protagonists and called it "The Slaver Weapon".
The result of this was it inject several Known Space elements into Star Trek. Kzin, or Kzinti, Slavers, Stasis boxes and the Kzin Wars. This has caused endless debate over whether any of this really fit into Star Trek or should, and where Kzin belong.
In order to avoid antagonizing Larry Niven, in Starfleet Command II , The Kzin were relabelled the Mirak, while in Deep Space 9, there was mention of a Tzenkethi which was taken by some to be reference to the Kzin.
See Felinoid Races of ST-OM for Jay's rambling on the subject