Who will be the new Dr Who?

Matt Smith will step down from the role at the end of this year.

The bookies always get it wrong. Every time a new actor is about to be named as the new star of Doctor Who, there are outrageous bets on familiar names and they always turn out to be wrong.

The announcement of the 12th Doctor tomorrow morning has been preceded by frenzied betting on actors like Peter Capaldi - who played the mighty Malcolm Tucker in The Thick Of It - or Chiwetel Ejiofor, or Joanna Lumley (perennial favourites for the first black or first female Doctor), but the role never goes to those kind of stars.

The actor, who will be revealed at 6am Monday morning (7pm NZ time), is far more likely to be some bright young thing who has played solid supporting roles in high quality productions, without ever really sticking in the mind.

It's not the role for an established actor, it's for somebody who wants to prove themselves.

Both David Tennant and Matt Smith had racked up impressive credits before they got the call from the Doctor Who production office, but it was the biggest role either of them had taken on.

They used it to ride a wave of immense cultural popularity, jumping off before it drowned them. Tennant will be back for the next special episode but has moved on with his career, while Smith has already shot a villainous role for Ryan Gosling's directorial debut.

The role of The Doctor is one of the biggest in modern television, with 50 years of history to be drawn on and compared with. All new Doctors are instantly judged by standards of the past 12, which include formidable and popular actors like Tom Baker and Tennant, and fierce fans of even the most unpopular Doctors.

Christopher Eccleston was the most high profile actor to take on the formidable role, but that was necessary for a new reboot, and once the concept of Doctor Who had reinserted itself into the modern collective consciousness, there wasn't any need for anybody bigger. The role is large enough for anybody.

Some people still think Doctor Who hasn't been the same since William Hartnell rejuvenated, but the whole concept of constant regenerations is a very good thing for Doctor Who, and a major part of the programme's extraordinary longevity.

Each time the series feels stale or tired, they bring in a new actor to play the lead role.

The Doctor is always a fiercely intelligent time traveller who always stands up to bullies, but he can have any personality and can be played in a variety of different styles, making it an easy role for new actors to slot into.

Jenna-Louise Coleman is sticking around as the current trusty companion for another few stories, to help ease the transition into another new era, but the programme itself regenerates with each new Doctor, breathing new life into this long story.

The new Doctor will be the 12th Doctor - although it might actually be the thirteenth, with John Hurt's mystery role in the upcoming 50th anniversary special promising some back-history fill-in - and the identity of this mystery actor will be revealed in just a few hours' time.

There is still the chance of a real surprise - a former actor returning to the role, or a change in gender or ethnicity - but it is more likely to be somebody who is ready to take off.

Whatever the result, Doctor Who's adventures in time and space go on and on.

* Visit nzherald.co.nz tomorrow morning for the announcement of the new Doctor Who.