Talk about it here.
The Doctor wore the ring on the middle finger of his right hand in his first incarnation, (TV: An Unearthly Child) but soon discarded it after his regeneration into his second incarnation, as it did not fit him any longer. (TV: The Power of the Daleks)
The ring had several special abilities. It could supply power to the TARDIS's main doors and control a Zarbi. (TV: The Web Planet) If given the correct spectrum of light, it could unjam a TARDIS's locking mechanism. (TV: The Daleks' Master Plan) The ring seemed to be able to facilitate hypnotism and protect the Doctor from electrical shocks. (TV: The War Machines) On the Ethereal homeworld, the Doctor used the ring to open an electronic lock. (PROSE: The Cloud Exiles)
It was discovered to have fallen into the TARDIS console following the Doctor's first regeneration, where it remained until it was recovered by his seventh incarnation, who decided to start wearing it again. (COMIC: The Chameleon Factor)
Behind the scenes edit
Following the Seventh Doctor's recovery of the ring in The Chameleon Factor, he was then seen wearing it in several subsequent Doctor Who Magazine comic stories.