Guttorm, in Norse mythology, stepson of King Giuki, and, in some accounts, murderer of the hero Sigurd. According to the Icelandic 'Poetic Edda' and 'Prose Edda', Guttorm treacherously slew the hero Sigurd at the instigation of Brunhild. After an argument with Sigurd's wife Gudrun, Brunhild realized that she had been tricked by Sigurd into marrying Gunnar. Brunhild did not know that Sigurd had been given a potion to forget that they had loved each other. In her hatred for Sigurd she tried to incite Gunnar and his brother Hogni to murder Sigurd. They were willing to kill Sigurd, but could not, as they had sworn oaths of brotherhood with him. Conspiring together, they put their young stepbrother Guttorm up to the crime, offering him gold as a reward, and infuriating him against Sigurd by feeding him the meat of serpents and wolves. They succeeded in convincing Guttorm to commit the bloody deed. According to the 'Volsunga Saga', the frightened Guttorm twice hesitated at the bedside of Sigurd and his wife. On the third attempt he stabbed Sigurd and killed Sigurd's 3-year-old son, Sigmund. But Sigurd awoke, and despite his mortal wound, he had enough strength left to throw his own sword, called Gram, at his attacker, severing Guttorm in two. Sigurd called out reassurances to his wailing wife, and died believing that her kin, his oath-brothers Hogni and Gunnar, would avenge his murder. In alternate versions of the story, all three brothers committed the crime, or Hogni alone carried out the treacherous deed.