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Origin, theories, and interpretations

Thor closely resembles other Indo-European deities associated with the thunder: the Celtic Taranis, the Estonian Taara (or Tharapita), the Baltic Perkūnas, the Slavic Perun, and particularly the Hindu Indra, whose thunderbolt weapon the vajra is an obvious parallels noted already by Max Müller. Scholars have compared Indra's slaying of Vritra with Thor's battle with Jörmungandr. Although in the past it was suggested that Thor was an indigenous sky god or a Viking Age import into Scandinavia, these Indo-European parallels make him generally accepted today as ultimately derived from a Proto-Indo-European deity.

In Georges Dumézil 's trifunctional hypothesis of Indo-European religion, Thor represents the second function, that of strength. Dumézil notes that as a result of displacements, he does not lead armies; most of the functions of Indra have been in effect taken over by Odin. Many scholars have noted the association of Thor with fertility, particularly in later folklore and in the reflex of him represented by the Sami Hora galles ("Good-man Thor"). For Dumézil, this is the preservation by peasants of only the side-effect of the god's atmospheric battles: the fertilizing rain. Others have emphasized Thor's close connection to humanity, in all its concerns. Scholar Hilda Ellis Davidson summarizes:

The cult of Thor was linked with men's habitation and possessions, and with the well-being of the family and community. This included the fruitfulness of the fields, and Thor, although pictured primarily as a storm god in the myths, was also concerned with the fertility and preservation of the seasonal round. In our own times, little stone axes from the distant past have been used as fertility symbols and placed by the farmer in the holes made by the drill to receive the first seed of spring. Thor's marriage with Sif of the golden hair, about which we hear little in the myths, seems to be a memory of the ancient symbol of divine marriage between sky god and earth goddess, when he comes to earth in the thunderstorm and the storm brings the rain which makes the fields fertile. In this way Thor, as well as Odin, may be seen to continue the cult of the sky god which was known in the Bronze Age.