In early Germanic paganism, *Wulþuz ("glory"; Old Norse Ullr) appears to have been a major god, or an epitheton of an important god, in prehistoric times. The term wolþu- "glory", possibly in reference to the god, is attested on the 3rd century Thorsberg chape (as owlþu-), but medieval Icelandic sources have only sparse material on Old Norse Ullr.
The Old English cognate wuldor means "glory" but is not used as a proper name, although it figures frequently in kennings for the Christian God such as wuldres cyning "king of glory", wuldorfæder "glory-father" or wuldor alwealda "glorious all-ruler".
The medieval Norse word was Latinized as Ollerus. The Modern Icelandic form is Ullur. In the mainland Scandinavian languages the modern form is Ull.
In chapter 31 of Gylfaginning in the Prose Edda, written in the 13th century by Snorri Sturluson, Ullr is referred to as a son of Sif (with a father unrecorded in surviving sources) and as a stepson of Sif's husband; the major Germanic god Thor:
Ull, Sif's son and Thór's stepson, is one [too]. He is such a good archer and ski-runner that no one can rival him. He is beautiful to look at as well and he has all the characteristics of a warrior. It is also good to call on him in duels.