Idun

Goddess of youth and spring. Idun (Idunn) was the keeper of the golden apples of youth that kept the gods young and immortal.

In the Lokasenna, Loki accused Idun of sleeping with her brother's killer. Who Idun's brother was, we don't know. There is no mention of even Idun's parents. It is for this reason that there is a possibility that Idun was originally a Vanir goddess, but became an Asynia (Aesir goddess) when she married Bragi, the god of poetry.

One story was that the giant Thiassi, builder of Valhalla, demanded from Loki the goddess Idun and her golden apples as payment. Loki abducted Idun and stole her basket containing apples for Thiassi. Without the apples, the Aesir began to age. During the council, the gods compelled Loki to bring Idun and the apples back.

Loki turned himself into a falcon and flew to Thiassi's home. Loki waited until Thiassi was distracted before entering her home. He changed Idun into a nut before fleeing back to Asgard. Idun returned with the apples, and the gods were restored to their youthful looks.

See the Apples of Youths in Of Thor and Giants.