Tarwildbaning was a Euterpian. He was part of a five member recon team (the other members being Atimkos, Godwanna, Thorsuun, and Udentkista) from the Euterpian mothership that landed on Earth around 40,000 BC. They planned to refuel the mothership from Earth's magnetic core, but before that happened, the mothership was destroyed by solar flares. The recon team were the only survivors. Their plans to destroy Earth in 1994 were defeated by the Second Doctor.
When they discovered their homeworld no longer existed, Udentkista and Tarwildbaning decided they liked their life on Earth, and helped to stop their fellow Euterpians' plans. (PROSE: Invasion of the Cat-People)