The god Ull probably belongs to the group of ritual gods. The facts to be drawn upon for the explanation of his character are firstly that he is called the stepson of Thor, and secondly that he is closely associated with a shield, and these two facts form parts of the same evidence.
The first datum indicates his place in the drama as the companion and helper of Thor — in the same way as Hoenir, but in different situations; in the Thorsdrapa the relationship between the two divinities is defined by a ritual word of unknown acceptation: gulli. The character of their cooperation is sufficiently indicated by the shield that plays a part in either drama, in the former the shield on which Hrungnir was slain, in the latter the shield that saved the companions of Thor from being drowned when crossing the infernal river.
The programme of these scenes is given by S E (115): “shield may be called the ship of Ull or paraphrased in allusion to the foot of Hrungnir”; from this note we learn that a shield was a ritual implement in the drama, and further that the functional divinity of this shield was called Ull. The passage in the legend of Hrungnir stating that the giant thrust the shield under his feet or, as Haustlong has it, that he was slain on the shield, indicates the ritual staging of the act. Probably the shield and the shield god, as Ull is poetically named, performed in situations other than those accidentally mentioned in mythological literature, as it has come down to us.
Grimnismál 42 adds one more item to our knowledge concerning the part played by Ull in the drama; the verse (v. supra p. 294) intimates that the god was connected with the sacrificial fire and the kettles. This hint is probably elucidated by Baldrs Draumar v. 7, whence it appears that the holy vat of ale was covered by a shield: “Here stands the mead brewed to welcome Balder, pure drink covered by a shield”. Further epithets belonging to Ull are bow-man, ski-runner, god of chase, but in default of explanatory legends or other hints, the significance of these names must be left undecided. The remark of S E (31) that he is worth calling on before entering on a duel probably hinges on his ritual role as Thor's helpmate.
So the knowledge of the god Ull must remain somewhat vague and circumstantial.
“The Culture of the Teutons”