Ring of Rassilon

From TARDIS Index File, the free Doctor Who reference.

The Ring of Rassilon was worn by Rassilon, who slept eternally in the Tomb of Rassilon while his mind lived on in the Matrix. Anyone who was to wear the Ring of Rassilon as told in the rhyme, written in Old High Gallifreyan.

To lose is to win

And he who wins shall lose

When the Ring is worn it grants the wearer immortality, imprisoning them in stone watching over Rassilon. (DW: The Five Doctors)