Norsum was a planet that was home to a race of giant green Space Vikings.
When Queen Angboda reigned as their queen, she banished three warriors, Thaur, Vulsturg the Vast and Jotastar the Just on separate primitive planets so they would longer be a threat to other civilised worlds. However, a teleporter ray from an unknown source, most likely the traitorous Vemnec, sent the three to planets that were populated. When one of the Norsum exiles, Thaur, encountered the Doctor, he tricked the Doctor into believing that Angboda was "building a warship to crush a hundred planets". (COMIC: Wrath of the Warrior)