In Norse Mythology
Reginn, often Anglicized as Regin or Regan, in Norse mythology, is a son of Hreiðmarr and foster father of Sigurd. His brothers are Fafnir and Otr. When Loki mistakenly kills Ótr, Hreiðmarr demands to be repaid with the amount of gold it takes to fill Ótr's skin and cover the outside. Loki takes this gold from the dwarf Andvari, who curses it and especially the ring Andvaranaut. Fafnir kills his father for this gold, but eventually becomes a greedy dragon. Reginn gets none of the gold, but he becomes smith to the king and foster father to Sigurd, teaching him many languages as well as sports, chess, and runes. He then sends Sigurd to kill his brother, Fafnir, in order to claim the gold. After Sigurd kills him, Fafnir's blood allows him to understand the language of birds. The birds give a warning to Sigurd that Reginn secretly plans on killing him and taking the treasure for himself. Consequently, Sigurd kills Reginn and keeps the treasure, though he himself eventually meets his own doom in the future.
In God of War (2018)
Reginn was captured by the Dwarf King and forced to act as Sentry of Konunsgard.