Species 29

Species 29 was a race of aggressive humanoids who took part in a large war with Species 7.

Biology
Species 29s were originally a humanoid race with purple skin and short, white hair which fell down across the back of their heads. Later, they were transformed into incorporeal life-forms by the Ageless. They were moved temporarily into the bodies of cats. Even while in these bodies, they retained their basic abilities, such as intelligence and mind reading. (DWS: Cats and Dogs)

Culture
The Species 29s were, according to the Doctor, the fourth greatest liars in the universe, behind the Sisters of Falsehood, the Decevions of the planet Fibb and Jeffrey Archer. (DWS: Cats and Dogs)

Technology
In their humanoid forms, Species 29 had a technologically advanced home-world, with large building made from an unknown black material and a green lighting. They also had battleships with large laser cannons mounted on top. (DWS: Cats and Dogs)

History
Species 29 were originally a humanoid species, who lived on a planet where everything was extremely organised. At some point in their history, they went to war against a fellow humanoid race, the Species 7. The war raged on for thousands of years, and at one point threatened to destroy the entire universe.

Eventually, a neutral race known as the Ageless intervened, using their superior technology to remove the minds of the species 29s from their bodies. They were kept in this incorporeal state for a thousand years, after which the Ageless decided to review their punishment with a trial. The Tenth Doctor was also present at the trial, as an additional party. The Doctor deliberately caused a transdimensional quirk which gave the species 29s real bodies, in the form of cats. The Species 29s attempted to go to war against the Species 7s - who had been transformed into dogs - and the Doctor advised the Ageless to not give the Species 29s their real forms back. (DWS: Cats and Dogs)