Large, ferocious dog-like animals used by the Klingon guards of the Rura Penthe penal colony to keep prisoners in line, seen in Star Trek VI: The Undiscovered Country.
Jackal mastiffs are heavily built, hairless quadrupeds with wide jaws full of teeth, kept on chains by the warders of the dilithium mines on the frozen asteroid Rura Penthe. With no fence around the camp, the cold and the animals are the main means of control.
They appear in Star Trek VI: The Undiscovered Country. When Kirk and McCoy arrive as convicts, the commandant addresses the new prisoners while handlers hold the snarling beasts close by, and the animals are seen again when the guards catch up with the two officers and the shapeshifter Martia on the surface.
The animals are not named in dialogue; the term comes from the film's script. They resemble, but are distinct from, the Klingon monster dog kept by Commander Kruge in Star Trek III.