In the lore of many ancient cultures from around the world, there exists an object or substance which grants the gods or heroes the gift of prolonged life or even immortality. Examples of these include the ambrosias of the Greeks, the divine peaches of the Chinese, the somas of the Persians, or the elixirs of other various traditions. The equivalent in Norse mythology is the golden apples, whose function was to return the gods to youth each time they aged.
The Goddess Iðunn (anglicised as Idunn) was one of the Æsir (Aesir), and keeper of the golden apples in Ásgarðr (Asgard). Her name itself means “rejuvenator” or “ever young”, and it is believed that she was also associated with fertility. She is attested in one poem to be descended from the Álfar (Elves), which might suggest that the longevity provided by the golden apples is derived from that race. While appearing in Eddas a number of times, the story in which Idunn features most prominently has her and the apples kidnapped by a giant. Her absence causes the other Aesir to grow grey and old, and face death. Only upon her rescue and return to Asgard are they revitalised to regain their youth. It is commented upon in the Prose Edda that the gods rely heavily on Idunn.