William Hartnell (1963-66)

When the veteran BBC producer Verity Lambert first outlined the role of Doctor Who to his first interpreter, William Hartnell, the actor was so enthused that he declared he believed the series could run for as much as five years. Hartnell worked hard. In its earliest days, the show went out 48 weeks a year.

He drew an immediate enthusiastic young following, so much so that when he was seen in public, he often found himself leading a column of devoted youngsters, “like the Pied Piper of Hamelin”. School students revising for physics O-levels would write to him asking him complex questions about the mechanics of the TARDIS and time-space ratios.

The part of Doctor Who was conceived as a mixture of equal parts dotty old granddad and absent-minded professor, and Hartnell brought exactly these qualities to the role – qualities that, with one or two notable exceptions, have been the common link among all the actors who have played him, no matter what their age or physique.

The first Doctor’s first assistants were his schoolgirl granddaughter, Susan Foreman (Carole Ann Ford), and two of her teachers, Ian Chesterton (William Russell) and Barbara Wright (Jacqueline Hill), who follow her home one evening after being puzzled by her behaviour at school. They are unwittingly led by her into the TARDIS, and thence to the earth in 10,000BC, where they must battle a race of primitive humanoids.

Through most of its TV career until its revival, the plotlines on Doctor Who lasted for several programmes, rather than each programme being its own stand-alone story. In only the second storyline of the Hartnell era, which began just before Christmas 1963, the Doctor’s arch-enemies, the Daleks, made their first appearance. This was the story that formed the basis for the first Doctor Who movie, Doctor Who And The Daleks (1965), in which the Doctor was played by Peter Cushing.

A later assistant of Hartnell’s Doctor, Steven Taylor, was played by the future Blue Peter presenter, Peter Purves.

Patrick Troughton (1966-69)

The second Doctor, Patrick Troughton, retained the fun side of the character, indulging in much fancy-dress clowning, and bringing to the role that slight edge of incompetence that succeeding Doctors have displayed. Troughton had received Hartnell’s blessing as much the best candidate for the job when the time came for him to move on.

Troughton played the Doctor as a “cosmic hobo”, a kind of intergalactic Charlie Chaplin with a wicked streak and an insolent attitude to authority. He was accompanied on his adventures by one of the Doctor’s relatively rare male assistants, Jamie McCrimmon (Frazer Hines), who had been rescued via time travel from the Battle of Culloden in 1746.

The Monster count during Troughton’s tenure was thrillingly high, with evil beings such as the sinisterly hissing Ice Warriors proving themselves a nuisance when the Doctor wasn’t battling either the Daleks or the Cybermen.

Jon Pertwee (1970-74)

With the beginning of the 1970s, the series format changed. The Doctor no longer had to battle the forces of evil for ten or 11 months a year, but was allowed a longer rest in between challenges.

New Doctor Jon Pertwee brought a distinctly swashbuckling note to the role. After the rather crumpled demeanour of Troughton, the Doctor became a bit of a dandy, with ruched dress shirts, skill in swordsmanship and a crowning silver bouffant hairdo all part of the image. As befitted this slightly preening look, Pertwee added a faintly petulant note to the role. Working within an organisation called UNIT, he found himself adrift among incompetent bureaucrats and wooden-headed military personnel who had shortened his temper. Only the feared Master, a fellow Time Lord gone to the bad, memorably played by Roger Delgado, gained the Doctor’s respect.

His assistants were glamour girls with a distinctly contemporary air. Jo Grant (Katy Manning) was a platform-heeled, much-bejewelled Carnaby Street girl-about-town who had survived from the Troughton era, while Sarah-Jane Smith (Elisabeth Sladen) was all gasping, breathless passion.

Tom Baker (1974-81)

Still for many the greatest Doctor ever to travel in time (until perhaps the modern era), Tom Baker was the longest-serving Doctor to date. Relatively youthful when he took up the role in 1974, he played the Doctor as a deceptive buffoon. Sweeping through plotlines in ankle-length scarf and Oscar Wilde hat, this Doctor was adept at poking fun at evil aliens, at least until things turned really nasty, when he would get impressively cross and serious.

As befitted a centuries-old Time Lord, he was always at least two mental jumps ahead of everyone else, so much so that for much of the time nobody knew what he was talking about. Nobody human, that is. One of the innovations of Tom Baker’s period in the role was the robot dog, K9, who always seemed to understand the Doctor’s instructions.

In addition to K9, there was also Leela (Louise Jameson), a warrior princess who had mistaken the Doctor for her tribal god. Leela’s feisty nature and preference for revealing clothing is thought to have boosted the teenage male percentage of the show’s audience even further.

Peter Davison (1981-84)

The fifth incarnation of the Doctor was played by Peter Davison. Despite his preference for dressing like a 1920s bright young thing, in jaunty blazer, deckchair-striped trousers, cricket jumper and Panama hat, Davison was the one Doctor of the pre-cancellation era (i.e. before the BBC dumped the show) not to be a hopeless eccentric. His Doctor was a straightforward, youthful, cheery soul with a core of deep-seated wisdom to him and more than a dash of cute.

A new slant on the role of the assistant was introduced in the colourful form of Tegan Jovanka (Janet Fielding), an air hostess who had wandered into the TARDIS in the mistaken impression that it really was a police phone box. She was followed by teenage American botany student, Peri Brown (Nicola Bryant).

Colin Baker (1984-86)

It was the misfortune of Colin Baker to take on the role of Doctor just as purists had started to bemoan the show’s decline. This Doctor appeared in pantomime costume and was equipped with a rather snarling temper, generally deemed too much of a culture shock after the mild-mannered likeability of Davison.

Drafting in a famous face to boost the drooping ratings, the BBC cast Bonnie Langford as new assistant Mel Bush, a computer programmer with a photographic memory. She bridged the Baker and McCoy eras.

Sylvester McCoy (1987-89 and 1996)

With the arrival of Sylvester McCoy in the role, the silliness factor went off the dial. The show was now being played as cosmic sitcom by an actor previously known as a zany frontman on children’s TV. We were back in the comic fantasy realms of Patrick Troughton. As McCoy got into his stride, however, he brought unexpected depth and ambiguity to the part, revealing a dark side that Troughton’s craggy looks had only deceptively hinted at 20 years earlier.

One of the best-loved assistants of the Eighties was Ace (Sophie Aldred), also familiar from children’s TV, who very often made something human and moving out of a role that had traditionally required not much more than pointing at monsters in quavering terror.

Paul McGann (1996)

McGann’s role in the show sounds like an eternal quiz question. Which actor only played the Doctor in a one-off TV film, but never in an ongoing series? The show had finally been committed to television history (or so it was thought) in 1989, but was speculatively revived in the curious form of the feature film Doctor Who (1996).

Paul McGann played the Doctor as though he were the romantic male lead in the costume adaptation of a little-known Victorian novel. There was a soft-focus quality to his delivery, as well as the silk cravat and nut-brown curls of a Brontë hero.

Christopher Eccleston (2005)

When Doctor Who was revived as an ongoing TV series in the spring of 2005, there were some raised eyebrows over the casting of Eccleston as the ninth incumbent in the role. Gone were the zany and foppish manifestations of the 1970s and 1980s, and in their place was a new hardcore Doctor, a crop-haired Action Man in leather coat, who lost no time in shouting his mind when confronted with his ancestral enemies.

The Doctor’s new assistant was Rose Tyler (Billie Piper), plucked from a humdrum London existence and a loyal boyfriend to go time-travelling. Those who doubted whether Piper – an ex-pop star and former wife of DJ Chris Evans – was quite up to the role were soon proved wrong. By common acclaim, she turned out to be a revelation, bringing genuine emotional depth to what was traditionally a fairly thankless role over two series.

David Tennant (2005- )

The current Doctor, unveiled in a Christmas special in 2005, is David Tennant, who had recently taken the title role in a dramatisation of the life of the legendary Italian philanderer, Casanova. Tennant has brought some of the unpredictable whimsicality back to the Doctor’s character, and a little of the 1970s dress sense. With a swishy long coat worn over brown pinstripe suit and Converse trainers, he combines the eccentricity of Tom Baker with the manic energy of Sylvester McCoy.

With Piper’s departure after two series, the Doctor’s current sidekick is Mickey Smith (Noel Clarke), a garage mechanic and boyfriend of Rose. Having initially been rather rudely unimpressed by Mickey (“Mickey the Idiot” was his pet name for a while), the Doctor has now remembered his manners, and has taken Mickey on as a valued and resourceful assistant who doesn't mind getting stuck into a fight.