In a parallel universe, the Klingon Empire was an interstellar empire led by the Klingons. Its capital was the First City on the Klingon homeworld Qo'noS. During the 24th century, it was allied with the United Federation of Planets.
In an alternate timeline shown to Captain Jean-Luc Picard by the Eleventh Doctor in 2368, the population of Qo'noS had been converted by the Cybermen. This timeline was negated by Jean-Luc Picard and the Doctor that same year. (COMIC: Assimilation²)