In Norse mythology, Víðarr or Viðarr (often Anglicised Vidar) is the son of Odin and the giantess Gríðr. He avenges his father's death. In the reborn world that arises after Ragnarök, Víðarr is preordained to return with his brother Váli.

During Ragnarök, Odin is eaten by the wolf Fenrir and Víðarr will avenge his death by killing the beast. According to the Vafþrúðnismál, Víðarr kills Fenrir by stepping on his lower jaw with his foot, on which he wears a iron shoe that his mother Grid made him. The shoes protected him from being devoured by Fenrir. Having his foot placed, he will take the wolf's upper jaw and tear the beast apart. According to the Völuspá however, he uses his sword to kill the wolf by driving it straight into its heart.