Grettis Saga, or The Saga of Grettir the Strong is one of the medieval Icelandic Sagas. The first part of the saga is utilized to describe Grettir's ancestors, who lived largely uneventful lives with the exception of Onund Treefoot, a viking warrior from whom Grettir is said to inherit his strength. When Grettir is young, he is intelligent and courageous, but also bad-tempered.

When a draugr named Glam is troubling the country, Grettir goes to fight it. The two have a long struggle but eventually Grettir is victorious. Glam, exhausted, curses Grettir. This is when his misfortunes begin. Grettir accidentally sets fire to an inn and several people die as an eventuality. He is soon condemned to be an outlaw.

Despite his bad luck, Grettir survives being an outlaw for an uncanny amount of time. His friends argue that he should be returned to the law's good graces and it is eventually agreed that once he has "served" twenty years as an outlaw, the sentence may be lifted. His enemies, however, use magic runes to cause Grettir to injure himself, making him an easy target. In the end, Grettir is finally defeated.