In the mirror universe, the Halkans were the species native to the planet Halka.

In 2267, the Halkans were exterminated by Captain James T. Kirk following his return to the ISS Enterprise as they had refused to share their planet's vast deposits of dilithium with the Terran Empire. Science officer Spock had tried to find a reason for sparing the Halkans as directed by Kirk's counterpart from the Federation universe; nevertheless, Kirk refused to listen and ordered their annihilation. (TOS episode: "Mirror, Mirror" and TOS novel: The Sorrows of Empire)