Tromos was a loba from Lobos who was experimented on. He was made stronger and larger than an ordinary loba. He was the only one who did not kill himself after the experiment. However, he was considered mad by many. He was held in a prison.
Mykados planned to use him as the Champion of the Temple of Tordos in a death match against the Thirteenth Doctor. In the confusion during the successful attempt of rebels to rescue the Doctor, Tromos took Ryan Sinclair hostage and ran away.