Species 7

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

Biology
Species 7s 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 temporarily moved into the bodies of dogs. Even while in these bodies, they retained their basic attributes, such as intelligence and mind reading. (DWAN: Cats and Dogs)

Technology
In their human forms, Species 7 had a technologically advanced home-world, with large building made from an unknown black material and green lighting. They also had battleships with large laser cannons mounted on top. (DWAN: Cats and Dogs)

History
Species 7 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 29s. 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 7s 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 present at the trial, as an additional party. The Doctor, however, deliberately caused a transdimensional quirk which gave the species 7s real bodies, in the form of dogs. The Species 7s attempted to go to war against the Species 29s - who had been transformed into cats - and so the Doctor advised the Ageless to not give the Species 7s their real forms back. (DWAN: Cats and Dogs)