In four years time Doctor Who will be 50 years old, but still it remains one of the most popular and imagination-grabbing shows on television. While the best of British actors and television writers are lining up to work on it, the series’ first appearance of 2009 – the Easter special ‘Planet of the Dead’ – is about to hit our screens, marking one of tenth Doctor David Tennant’s and showrunner Russell T Davies’ final adventures before their respective replacements Matt Smith and Steven Moffat take over in 2010.

Before any of that, though, a nationally-franchised exhibition of costumes and props is coming to Kelvingrove for an eight-month run, joining similar permanent and temporary displays in Cardiff, Blackpool, Land’s End and Coventry. With former Eastenders and Bionic Woman star Michelle Ryan and Brit comedy actor Lee Evans declaring their excitement at being involved in the new special, the great British public’s fascination with all things Who shows no sign of passing. So how has the Doctor done it? How has an eccentric alien with two hearts and a blue police box snared the nation’s imagination for half a century (give or take the 1990s)?

The answer, in more ways than one, seems to be regeneration. ‘One of the smartest things about the show is the way it’s developed,’ says Stephen Greenhorn, the Scottish creator of River City and Sunshine on Leith: The Musical, and also the writer of two episodes of ‘new Who’. ‘There’s this in-built logic about how the actor playing the Doctor will change so that the show can reinvent itself. Beyond that, the series thrives on having a vivid, exciting central character who owns a machine that gives him a certain capability to travel to any place and any time. As a writer, this gives you access to any kind of story you want. You’re never going to run out of things to say or do.’

The all-action, big-budget and critically-acclaimed current version of the show has created its own mythology and set a unique benchmark for family entertainment television in the UK since its 2005 return. Yet the original series, which ran from 1963–1989, built up enough weight of iconography that nothing needed to be substantially tinkered with, even if CGI sets are preferable to wobbly plasterboard for all but nostalgia’s sake.

‘When the show first began it was engineered to be educational as much as it was entertaining,’ says David Bishop, a lecturer in creative writing at Edinburgh Napier University, former editor of seminal Brit sci-fi comic 2000AD and writer of four novels and many audio dramas set in the Doctor’s world, including the forthcoming Enemy of the Daleks. ‘In the days of William Hartnell, the first Doctor, there would be a mixture of science fiction stories set in the future and on alien worlds, alongside historical stories where the TARDIS would go to the time of the Aztecs or the French Revolution, with the aim of educating a younger audience.

‘What really made the show hugely successful, though, were the Daleks. They were in the second story ever broadcast, and they basically turned Doctor Who into an overnight sensation.’ This is something which is still reflected today in the new Who exhibitions, with costumes and props for the most famous baddies, including the Daleks and Cybermen, taking centre stage alongside interactive displays which detail the show’s behind-the-scenes workings, including the costume, make-up, set design and special effects departments. ‘When my father Bernard ran the special effects department for the BBC they held an exhibition at the Science Museum around 1971, which was swamped by kids who only wanted to see the Daleks,’ says Martin Wilkie of Experience Design, designer of the exhibition on behalf of BBC Worldwide. ‘That was the initial inspiration for the Doctor Who exhibition, which has existed in one form or another pretty much ever since.’ Indeed, the most famous Who show at Longleat ran for 31 years before closing earlier this decade.

The Beeb took note of the public’s love for monsters. With the best intentions, the historical romps faded in favour of Cybermen, Ice Warriors and yet more Daleks as the 60s progressed. It’s been like that ever since: ‘When I came on board they were at pains to point out that the new show is an action adventure for all the family,’ laughs Greenhorn, ‘and at no point was there an educational remit! In fact, a scientist following the modern Doctor Who would probably be somewhat distressed by the “science” in there. You can still talk about bigger issues within the format, though. One of my favourite early stories is “The Green Death” (1973), which is about the environment, globalisation and the destruction of mining communities, while the first episode I wrote (2007’s “The Lazarus Experiment”) involves a moral conversation between a scientist who wants to be immortal and a man who actually is immortal, the Doctor.’

Greenhorn touches on another aspect of the Who experience by declaring himself a child of the early 70s’ Jon Pertwee years, in that whichever Doctor someone watches at a certain age or with a certain regularity becomes ‘their’ Doctor. ‘He was a kind of manic, gadgety, James Bond-type mad professor; I loved all that. Of course, in those days you didn’t have 57 channels and all manner of recording devices. There were three channels and no way of getting it back if you didn’t sit down with your family on Saturday and watch a show like Doctor Who. And if you didn’t, you’d have nothing to talk about in the playground on Monday morning.’

With the kind of imperious swagger which only men wearing improbably long scarves and sticks of celery on their cricket whites can muster, the series strode on through the Tom Baker and Peter Davison years, until the 1980s saw the show’s popularity finally waning. ‘By the time the series approached the end of that decade,’ says Bishop, ‘it had been going for a quarter of a century and was running out of juice, basically. It wasn’t getting the budget it needed to continue as a cutting edge sci-fi show and was being treated as an afterthought by the BBC, being scheduled up against Coronation Street. That was the equivalent of sending out a small boy to play against Man United, and Doctor Who got crushed.’

Excepting a Paul McGann-starring TV movie in 1996 and the odd Children in Need appearance, that was it for 16 years. So why did the Doctor eventually make a comeback when he did? Bishop has only one over-riding answer: ‘It was just waiting for someone to come along with the creativity, the wit, the nous and the will to revive this lost icon of British television – and, fortunately, Russell T Davies was the man selected. He’s managed to keep what was best about the original series and bring it bang up to date with some great writing and the money to make it actually look good on screen.’

Oh, and there is one other figure who has been most instrumental in the show’s success; ‘John Smith’, the good Doctor himself, an enduring British hero to rival James Bond, Robin Hood or Sherlock Holmes. ‘We’ve all grown up with a version of him,’ says Greenhorn, ‘and even the younger generation have now known him for four or five years. So there’s the sense that you should know who he is, but what I love about Doctor Who is that the character’s constantly shifting, constantly surprising you; he’s just familiar enough to trust, to welcome in as a hero, but there’s always the reminder that he’s a 900-year-old alien with an enormous intellect who knows things we could never understand. He’s a mystery, a complete unknown, but you know he’ll make things alright in the end.’

For Matt Smith, the youngest ever incumbent and just six years old when Sylvester McCoy left our screens in 1989, the Doctor Who challenge will be about as tough as it was for the ten (official) actors who preceded him. Whichever way it goes, though, we reckon the Doctor will survive.

The Dr Who Exhibition is at Kelvingrove Museum and Art Gallery, Glasgow, Sat 28 Mar–Mon 4 Jan 2010. ‘Planet of the Dead’ will be screened on BBC 1 on or around Easter Sunday.