Czar U'thai was the leader of an Asian tribe of warriors in 11th century Europe.
U'thai and his men raided villages and towns, killing and laying waste to the towns and taking away the young women. The evidence of their attacks could be seen all over the countryside.
As U'thai prepared to attack the town led by Udilf, he was visited by the Fifth Doctor and Adric. He let them live and fed them in return for the Doctor performing a few magic tricks for his entertainment.
When U'thai and his men attacked the town, they were unafraid of the tricks that the Doctor had prepared to frighten them away. They killed many of the townspeople, and attempted to take several of the women, including Tegan, but the townspeople were able to fight back with the longbows introduced by Adric. The Doctor pinned U'thai to a tree and offered mercy to U'thai and his men. (PROSE: The Immortals)