Klingon

In a parallel universe, the Klingons were a species from the planet Qo'noS who were the leaders of the Klingon Empire.

Biology
The Klingons were humanoids with ridged foreheads. (COMIC: Assimilation²)

History
During the 24th century, they were allied with the United Federation of Planets. One Klingon, Worf, was a Starfleet officer who served on the USS Enterprise-D in the 2360s. Some Klingons were assimilated by the Borg Collective; at least one Borg of Klingon origin appeared aboard Locutus' cube during the Battle of Wolf 359, another was seen following the fallout of the Borg-Cyberman Alliance. (COMIC: Assimilation²)

Alternate timeline
In an alternate future shown to Captain Jean-Luc Picard by the Eleventh Doctor, the Cybermen, using Borg technology, conquered Qo'noS and converted the entire populace into Cybermen. (COMIC: Assimilation²)

Behind the scenes

 * The Klingons are one of the major races of the Star Trek universe. They have appeared many times in all seven television series and all but two of the films.
 * In the Top Gear "Master of the Universe" segment, a Klingon raced around the Top Gear track against a Dalek, a Cyberman and Colin Baker as the Sixth Doctor (as well as Darth Vader from Star Wars and Ming the Merciless from Flash Gordon).
 * In the Doctor Who television story The God Complex, a woman in Howie Spragg's room on the prison ship which held the Minotaur asks Howie how to say "loser" in the language "K-K-K-Klingon". Though The God Complex doesn't make a direct connection to the race, this is an obvious reference to the language spoken by the Klingons.
 * J. K. Woodward, who worked on the Star Trek crossover Assimilation², released a piece depicting River Song dressed as a Klingon holding a bat'leth.