Otr or Otter, son of Hreidmar was a dwarf in Norse mythology.

According to the Prose Edda, he could change into an any form, and used to spend his days in the shape of an otter, greedily eating fish. Otr was slain accidentally by Loki. Hreidmar demanded a large weregild for Otr's death, namely to fill Otr's skin with yellow gold, and to then cover it entirely with red gold. When the skin was covered, one whisker was still protruding, forcing Loki to give up his ring Andvarinaut to hide it.

See also Andvari, Der Ring des Nibelungen