Entusso was a planet prone to alien invasion.
The Eighth Doctor and Sam visited Entusso and stopped many alien invasions during their visit. After these visits, the people of Entusso saw the Doctor as a hero and treated him as the defender of their world.
Later the Doctor visited Entusso again with his companion Fitz and found that a company called Alien Defence Incorporated (ADI) had used the Doctor's image to gain money for protection from aliens. The Doctor and Fitz put a stop to this and made sure that ADI built their reputation themselves. (AUDIO: Fitz's Story)