Shoju

Shoju was the name of an alien traveller from the stars whose natural form was that of a dragon. He sought a simple existence and came to a tiny 13th century Japanese village. But the villagers were fearful of him and so he used a chameleon device to hide himself amongst them, claiming to be a samurai. He was allowed to stay if he could get rid of the dragon (himself) and stop the flooding (caused by his chameleon device), but he was unable to do so. With the Doctor and Amy Pond's help, the Doctor managed to break the chameleon device, leaving Shoju stuck in a human form. With the dragon no longer a threat to the villages, Shoju found his new home in the village. (DWA: Samurai's Secret)