Ulf was a Viking who took part in an attack on Wulnoth's village in Northumbria in 1066. He and several others fought with Wulnoth and his men. When only he and Sven survived, Ulf wanted to hide in the monastery.
In the monastery, he and Sven caught the First Doctor and imprisoned him. However, the Monk sneaked up behind Ulf, knocked him out, and tied him up. After Sven found him, they captured the Monk, who informed them he was setting up a beacon for their fleet. As they helped him set it up, however, they were surrounded by the Saxons and then killed by them. (TV: The Time Meddler)