A number of sources claim Loki to have originally been a fire god of some description. This, for instance:
Loki was originally a fire deity before he became more closely associated with the trickster archetype, and this better explains the odd story of conception. Farbauti, meaning “fierce strike”, was a representation of lightning. Nal meant “pine needles”, and her other name, Laufey, meant “leaves”. In this way, Loki – fire – was created by Farbauti – lightning – striking Nal or Laufey – pine needles or leaves.
Loki appears as a fire god (Loge) in Wagner's Ring Cycle, as well.
However, I've also read that this is a mistake, caused by the similarity between the names Loki and Logi, who is a personification of fire, as seen together in the Prose Edda:
So it was also with the games, in which ye did contend against my henchmen: that was the first, which Loki did; he was very hungry and ate zealously, but he who was called Logi was "wild-fire," and he burned the trough no less swiftly than the meat.
Was Loki really once considered a fire god?
(On a related note, does Farbauti's name ("fierce striker") really refer to, or could it reasonably refer to, a lightning strike?)