What kind of Doctor will Capaldi be?
The more things change the more they stay the same.
Nothing could be truer of Doctor Who who has been played by 11 actors since the first episode aired on the BBC on November 23, 1963.
On Christmas Day, when the show will celebrate 50 years, one month and two days, fans old and new with casual viewers will be invited to a funeral and a birthday party.
We'll mourn the death of Matt Smith's 11th Doctor, and celebrate the birth of Peter Capaldi's 12th Doctor.
It's called regeneration, a trick of the Doctor's people the Time Lords of Gallifrey, that ensures their survival where other races would wither and die.
It's one of the things that ensured Doctor Who survived as a show for so long. It is the reason why Matt Smith's Doctor was a millennium-old man in a gangly young man's body.
Smith, at 26, was the youngest actor to win the role. As a result his Doctor was the most physical of the 10 before him to pilot the stolen Type 40 TARDIS through the time vortex.
Nine and 10, Christopher Eccleston and David Tennant, would come a close second and third but neither had the Mr Tickle elasticity of Smith's Doctor which when coupled with show runner Steven Moffat's sometimes madcap scripts made him the most interesting Doctor to date.
He was capable of such wisdom and naivete at the same time.
Don't get me wrong, Eccleston's hard man in a leather jacket was the right way to reintroduce the show to old fans and win a new audience in 2005. It had been off air for 16 years, except for a failed North American TV pilot, and fans of the original show such as Russell T Davies had grown up and were now in a position to bring it back.
Tennant's pinstriped everyman Doctor was a welcome change from Eccleston, and was perhaps the best actor to have ever played the role until Smith came along and just nailed it as "a madman in a box".
That sentence is actually hard to quantify because so many of the original Doctors, from No 2 Patrick Troughton on, were just wonderful.
Smith captured so many of their idiosyncrasies which is what made him great. What Capaldi, 55, will bring to the role remains to be seen.
Before we see him on screen we'll learn how John Hurt's disowned regeneration of the Doctor, glimpsed at the end of the Season 7 finale, The Name of the Doctor, fits into Doctor Who lore and whether he is responsible for the fall of 11.
The 50th anniversary special, to air in the Britain on November 23, will deal with that and bring back Tennant and Billie Piper as his companion Rose.
There are all sorts of theories out there but Moffat's recent confirmation of the Doctor's limit of regenerations to 12 means that Hurt's Doctor must be responsible for stealing some regenerations from other Time Lords before they were killed in the Time War and that he fits somewhere between Paul McGann's Doctor 8 and Eccleston's Doctor 9. This actually makes Eccleston 10, Tennant 11 and Smith 12. Unluckily for Capaldi, then as 13.
But from the clips I have seen of him on YouTube Capaldi will bring something new and fresh to the programme, an older mercurial Doctor, which has not been seen since 2005.
But from the way he stood grasping the lapels of his jacket in this month's BBC Next Doctor special he might just hark back to the first actor to play the role. William Hartnell, who was also 55 when he created the role, stood the same way.
It's likely that Capaldi's Doctor will do more running and fighting than Hartnell's professorial Doctor, but he is also likely to be more of an all-rounder than some of his predecessors.
His casting proves Doctor Who has grown up. Older fans will definitely go with the show, but it remains to be seen whether the new legions of teenagers who came on board in 2005 will stay loyal.
Capaldi is such a canny choice that they just might.