Höðr is Odin’s son, Baldr’s brother, and blind. Snorri says of him only that he is strong enough, that the gods would rather his name never had to be mentioned, and that his handiwork will be long remembered — an introduction that is entirely about what he is going to do.
What he does is throw. When Frigg has taken an oath from every thing in the world not to harm Baldr, the gods make a game of the result: they stand Baldr in the middle of the assembly and shoot at him, strike him and throw stones, and nothing touches him. Höðr stands outside the ring, because he cannot see and has nothing to throw. Loki, having learned from Frigg that she passed over the mistletoe as too young to swear, puts a shaft of it in his hand and points him.
Varð af þeim meiði, er mær sýndisk, harmflaug hættlig, Höðr nam skjóta
“From the branch which seemed so slender and fair Came a harmful shaft that Hoth should hurl.” — Völuspá 33, tr. Bellows
The dart goes through Baldr and he falls dead — in Snorri’s account the worst deed ever done among gods and men. And then nothing happens, which is the strange part: the gods are on holy ground where blood may not be shed, and they can only stand and weep and look at one another. The reckoning is deferred, and when it comes it is not delivered by any of them. Odin fathers Váli expressly for it, and Váli, one night old, having neither washed his hands nor combed his hair, kills Höðr and carries him to the pyre.
The moral weight here is peculiar and worth sitting with. Höðr is blind, is handed the weapon, is aimed, and does not know what he is throwing or at whom; by any standard the wiki’s other cultures would recognise, the killer is Loki. Yet the punishment falls on the hand rather than the mind behind it, and it falls automatically, without trial or hesitation. Saxo Grammaticus tells a completely different story in which Høtherus is a mortal hero, a rival suitor for Nanna, and kills Balderus in fair combat over her — a version with no blindness, no mistletoe and no Loki, in which Höðr is simply the better man. That two accounts this far apart survive suggests the blind brother was already an old and unstable figure by the time either was written down.
He is not gone for good. In the vision of what follows Ragnarök, the surviving gods return to the field where Asgard stood, and Baldr and Höðr come back together from the realm of the dead and sit down in peace. Whatever was owed has been paid, and the pair the story spent its length separating are restored as brothers.