A changeling, also historically referred to as an auf or oaf, is a human-like creature found throughout much of European folklore. A changeling was a substitute left by a supernatural being on kidnapping a human being. Sometimes the changeling was a 'stock', more often the changeling was a supernatural being made magically to look like the kidnapped human. Supernatural beings blamed for stealing children included fairies, demons, trolls, nereids and many others. Usually, the kidnapped human was a child; but there were cases, particularly in Scandinavia and Ireland, where adults were taken.

The third season of Supernatural, an American dark fantasy television series created by Eric Kripke, premiered on October 4, 2007, and concluded on May 15, 2008. Traveling throughout America, protagonists Sam and Dean Winchester use their father's journal to help them carry on the family business—saving people and hunting supernatural creatures. The season begins with the brothers tracking down the demons released from Hell in the previous season finale. They become allies with a demon named Ruby, who claims to know a way to release Dean from his demonic pact—he had sold his soul to a demon and was given a year to live in exchange for Sam's resurrection—and wants to protect them from the new demonic leader Lilith. As Dean's deadline approaches, their efforts are further hindered by Bela Talbot, a professional thief of occult items who is often at odds with the Winchesters.