The Great Key of Rassilon


 * The Great Key is sometimes used to refer to the Rod of Rassilon

The Great Key (also known as the Great Key of Rassilon) was one of the Artefacts of Rassilon, which was never (except in rare circumstances) in possession of the Lord President, the Chancellor typically held the Great Key. A forbidden weapon known as the De-mat Gun was activated by the Great Key. (DW: The Invasion of Time)

Near the end of the Last Great Time War the Key was taken to a planet where the Doctor was being held prisoner. The Doctor escaped and stole the Great Key, intending to create a modified De-mat Gun that would wipe out millions from time and space at once by using the Medusa Cascade. (IDW: The Forgotten)