Doctor Who: A brief history of Gallifrey on screen

When was Gallifrey first introduced?

The first time we saw the planet was in 1969 serial The War Games, during Patrick Troughton's stint as the Doctor - but it had not yet been mentioned by name at this point. You have to jump forward to 1973 serial The Time Warrior, with Jon Pertwee now in control of the TARDIS, for the first instance of the word Gallifrey being used.

However, by and large, Gallifrey does not appear with any great regularity in the classic series - and is referred to relatively fleetingly throughout the original run. It takes on far more significance, as far as on-screen storylines are concerned, during the revived series from 2005 onwards - more on that further down the page.

What is Gallifrey and its inhabitants like?

The planet is characterised by its yellow-orange look from Space, and has historically been protected by an impenetrable barrier called the quantum force field. Although much of the planet consists of red grassy wasteland and wilderness, Gallifrey's principal city, known as The Capitol or Citadel, is a much more civilised location - and was once home to a substantial population of Time Lords.

The city is protected by a shiny glass dome and consists of many tall, shining towers. Other locations on Gallifrey include the Academy, where the Doctor, the Master and assorted other Time Lords completed training, and the second city of Arcadia.

As far as the population goes, Gallifrey is most famously home to the Time Lords - the race to whom the Doctor is a member. Time Lords resemble humans as far as their outward appearances are concerned, but as a species they have a number of notable differences including the ability to regenerate and the fact that they have two hearts. It is generally believed that while all Time Lords are Gallifreyan, not all Gallifreyans are Time Lords.

What happened in the Time War?

Gallifrey really begins to play a central role in Doctor Who at the advent of the revived series - and central to this is the concept of the Time War. During Christopher Eccleston's brief stint as the Doctor, he revealed that the planet had been destroyed - and nearly all the Time Lords wiped out, as a result of a massive conflict between their species and the Daleks.

During the David Tennant era, Gallifrey is referenced by name in the 2006 Christmas special The Runaway Bride and in series three episode Human Nature, before appearing for the first time in a flashback in a later series three episode, The Sound of Drums. Here we see, the Master initiated into the Time Lord Academy as an eight year old.

In Tennant's final episodes, the two part Christmas Special The End of Time, Gallifrey plays its most important role to date. The special features a plot in which the Master wishes to bring the planet out of a Time Lock that it has been in since the Time War - which would see the planet reemerge but would risk the Time Lords destroying time and the rest of the universe just to ensure their survival, with Lord President Rassilon believing this would see them rise to a new level of existence.

During the episode the Doctor realises that his earlier incarnation had fought against the other Time Lords during the Time War to prevent this precise plan from coming to fruition, and he eventually works with the Master to stop it again. The episode sees the Doctor come to realise that his home planet is a very different place from the one he remembers from his youth - and that the other Time Lords had used some despicable practises in their fight against the Daleks.

The next prominent episode featuring Gallifrey is the 50th anniversary special, The Day of the Doctor, from 2013, which explores the last day of the Time War, when we are lead to believe Gallifrey was destroyed. However instead we see the Tenth Doctor, the Eleventh Doctor and the War Doctor, along with Clara Oswald, decide against destroying Gallifrey, instead opting to freeze the planet in time within a parallel pocket universe.

In the 2013 Christmas special The Time of the Doctor, Matt Smith's last episode as the Time Lord, the rest of the Time Lords are seen attempting to re-enter the universe through a crack in the Universe on the planet Trenzalore, where they are currently stuck, with the Doctor wishing to keep the inhabitants safe without releasing them and bringing about the onset of another Time War.

At the end of the episode, hundreds of years later in the chronology, Clara Oswald is able to reach the Time Lords and persuade them to give the ailing Doctor another regeneration cycle. As she does so the crack closes forever, apparently leaving the Time Lords lost.

Much of Peter Capaldi's stint in the TARDIS involves trying to find the lost Gallifrey, and he is led astray by Missy - who erroneously tells him that Gallifrey is now located at its original coordinates. In the series nine finale Hell Bent, it becomes clear that the planet is now situated far into the future - close to the end of the universe - for its own protection.

The 12th Doctor travels there and deposes and exiles Rassilon before we see the planet in a much later period towards the end of the episode - now almost entirely abandoned. It is now populated only by the human immortal Ashildr, who is protected in the Cloisters beneath the Citadel.

What’s been going on with Gallifrey this series?

That's a very good question - throughout this series we've frequently seen Jodie Whittaker's Doctor plagued with visions of her home planet - but even she is unable to work out exactly what has gone on.

The visions date back to the beginning of series 12: towards the end of two-part series opener Spyfall she returns to the planet and finds it completely destroyed, along with a message from Sacha Dhawan's Master claiming that it was he who brought about the destruction.

With the Master reappearing at the end of last week's episode, hopefully the series finale will give us some definitive answers about how, and for that matter why, the destruction came about...

Doctor Who airs on BBC One at 6:50pm on Sunday 1st March