Secret Keeper

A Secret-Keeper is a person designated to keep a secret by means of the Fidelius Charm. The Secret-Keeper is the only person who is capable of revealing the protected information to others, either by informing them orally or by writing it down. This individual will become bound by the Fidelius Charm as well. If a Secret-Keeper dies, all the people already aware of the secret information become Secret-Keepers.

Known Secret-Keepers

 * Peter Pettigrew was the Secret-Keeper for James and Lily Potter after they went into hiding during the First Wizarding War with their infant son Harry, keeping their whereabouts in Godric's Hollow a secret. However, Pettigrew was secretly a traitor to the Order of the Phoenix. He informed Lord Voldemort of the Potters' location, resulting in the murders of James and Lily and Voldemort's first defeat when the Killing Curse rebounded from Harry. Because others believed that Sirius Black had been the Potters' Secret-Keeper, he was blamed for the betrayal and imprisoned in Azkaban for it without a trial.
 * Albus Dumbledore was the Secret-Keeper for 12 Grimmauld Place, the Headquarters of the Order of the Phoenix, until he died in 1997 . This forced the Order to abandon it, as they believed Severus Snape to be a traitor and he knew the location.
 * In 1997, after Harry Potter, Ron Weasley, and Hermione Granger infiltrated the Ministry of Magic, they escaped to 12 Grimmauld Place, but Yaxley grabbed Hermione as the trio Apparated to the house, thus revealing it to him.
 * In 1997 and 1998, the Order of the Phoenix used many safe houses, including the Burrow, Shell Cottage, and the Tonks House, all of which were under the Fidelius Charm and maintained by various Secret-Keepers.

Behind the scenes

 * Severus Snape once said that when a Secret-Keeper tells someone the secret, this person is bound by the Fidelius Charm and cannot tell anyone else . However, Ron Weasley was able to tell Dobby where Shell Cottage was, despite the fact that it was under the Fidelius Charm, with Bill Weasley as the Secret-Keeper . Possible explanations for the descrepancy are that Ron himself was also a Secret-Keeper, that house-elves such as Dobby have ways around magic protection and concealment, or that the Fidelius Charm was not yet in effect at that time.