The name Sigar can refer to three people in Scandinavian mythology, surrounding the legends of Sigurd the dragon slayer. One of them only appears as the friend of Helgi Hjörvarðsson in the eddic lay Helgakviða Hjörvarðssonar. The other two appear as the villainous members of the same clan in several sources.
Gesta Danorum
In Gesta Danorum (book 7), Saxo tells that Sigar had a daughter named Signy. Sigar was in a feud with Haki's brother Hagbard, but was informed by Signy's handmaid, that Hagbard had a secret love affair with Signy. Sigar decided to hang Hagbard, who, however, managed to inform Signy of this. Signy set her house on fire and succumbed in the flames while Hagbard executed himself in the gallows. Sigar tried in vain to save both Hagbard and Signy but failed. His only consolation was to bury the treacherous maid alive.
Gesta Danorum disagrees with the other sources by presenting Sigar as the son of Sywaldus, who was the son of Ungvinus, a Geatish king who became the king of Denmark.