During the funeral of the Norse God Baldur, The Gods had great difficulty in dragging the funeral ship “Hringhorni” into the sea. Knowing this level of strength could only be accomplished by a Jötunn (Giant) it was then the Giantess Hyrrokkin was summoned to Asgard to accomplish this task. It is said that when she arrived and began dragging the massive ship to the sea she did with such ferocity it cause the rollers under the ship’s keel to create sparks of fire. This enraged Thor so much he reached for his Mjölnir to strike her down but due to her getting the ship launched into the sea, the Gods asked he give mercy.
Hyrrokkin ‘the one who has withered from fire‘ is only mentioned in the Skáldskaparmál where it is said she is killed by Thor and in the list of Troll-wives in the Nafnaþulur. Much like Jarnsaxa, Hyrrokkin also rides a large Wolf and it is believed that she is the actual mother of Sköll and Hati which are sons of Fenrir.
Snorri’s Edda, Gylfaginning 49: “The Æsir took the body of Baldr and brought it to the sea. Hringhorni is the name of Baldr’s ship: it was greatest of all ships; the gods wanted to launch it and make Baldr’s pyre thereon, but the ship would not stir. Then word was sent to Jötunheim and in response, came a giantess named Hyrrokkin (Fire-smoked). She rode up on a wolf with a serpent for a bridle, and leapt off the steed. Odin called four berserks to subdue it; but they were not able to tame the steed until they had felled it. Hyrrokkin went to the prow of the ship and thrust it out on the first push, with such force that fire burst from the rollers and all lands trembled. Thor grew angry and clutched his hammer, and straightaway would have broken her head, had the gods not prayed for peace for her.” SOURCE