Loki Laufeyjarson is the god of mischief in Norse mythology, a son of the giants Fárbauti and Laufey, and foster-brother of Odin. He is described as the "contriver of all fraud". He mixed freely with the gods for a long time, even becoming Odin's blood brother. Despite much research, "the figure of Loki remains obscure; there is no trace of a cult, and the name does not appear in place-names".

Like Odin (though to a lesser extent), Loki bears many names : the Sly-One, the Sly-God, the Shape-Changer, the Trickster, the Sky Traveller, the Sky Walker, the Lie-Smith, among others.

The composer Richard Wagner presented Loki under an invented Germanized name Loge in his opera Das Rheingold--Loge is also mentioned, but does not appear as a character, in Die Walküre and Götterdämmerung.

he trickster god is a complex character, a master of guile and deception. Loki was not so much a figure of unmitigated badness as a kind of celestial con man. He would often bail out the gods after playing tricks on them, as illustrated by the myth in which he shears Sif's hair and then replaces it, or when he is responsible for the loss of Iðunn's apples of youth and then retrieves them again. Loki is an adept shape-shifter, with the ability to change both form (examples include transmogrification to a salmon, horse, bird, flea, etc.) and sex.

According to some scholarly theories Loki is conceived of as a fire spirit, with all the potential for good and ill associated with fire. However, this view is probably due to linguistic confusion with logi "fire", as there is little indication of it in myth where Loki's role is predominantly associated with Odin, either as Odin's wily counterpart or antagonist.

Ström identifies the two gods to the point of calling Loki "a hypostasis of Odin", and Rübekeil suggests that the two gods were originally identical, deriving from Celtic Lugus (the name of which would be continued in Loki). In any case, the figure of Loki was probably not a late invention of the Norse poets but was rather descended from a common Indo-European prototype.