Atimkos was a Euterpian. He was part of a five member recon team 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 (Atimkos, Godwanna, Thorsuun, Udentkista, and Tarwildbaning) were the only survivors. Their plans to destroy Earth in 1994 were defeated by the Second Doctor.
Atimkos unintentionally killed himself when he tried to sing himself out of the TARDIS after the Doctor had removed the Time Vector Generator to revert it to a simple police box; the ship was still indestructible even in this state, with the result that the outer shell reflected the sound of Atimkos's song back at him. (PROSE: Invasion of the Cat-People)