The Doctor is on his way out.
Oh, there'll be another one along soon, because that's the tradition of Doctor Who. The world's longest-running science-fiction TV series, it has featured 10 actors in the title role since 1963.
But for David Tennant, whose long goodbye continues Saturday as BBC America airs the second of his four final Doctor Who specials, The Waters of Mars, his four-year tenure as a wisecracking 900-year-old "Time Lord" who travels time and space in a 1950s London police call box known as the TARDIS is drawing to a close.
"It's hard, because I've genuinely loved doing it," Tennant said in an interview last summer.
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"I'm really proud of what we've done. It's difficult to step away from that. But at the same time, well, better to whilst I'm still loving it, better to leave them wanting more," he said. "And the show's in very rude health, so it's nice to be able to hand that on, to know that we've acquitted ourselves well."
For Americans who might have missed both the original Doctor Who, which aired in Britain from 1963 to 1989, or the slicker revival that writer Russell T Davies has overseen since 2005, it can be difficult to grasp just how important the series has been to generations of Britons. Or how popular it has made Tennant, 38, a Scotsman probably best known in the United States for playing Barty Crouch Jr. in Harry Potter and the Goblet of Fire and for a recent turn as the host of PBS's Masterpiece Contemporary.
"You all are much easier than the British press," he said to me after we'd wrapped up our interview, one of a series he was doing that day.
The remark briefly stung — reporters never like to hear that they're easy — until I remembered how closely his personal life gets tracked in Britain, where on vacation a few weeks later, I saw photographs and caricatures of him in the windows of half the souvenir shops I passed.
"Back home ... it's kind of the No. 1 drama," Tennant said. "It's nice to feel that we've done our job, and we haven't messed it up."
It's also a luxury for an actor looking to move on and to know he can go on to new projects without destroying the show he leaves behind. Tennant is reportedly starring in an NBC pilot for a comedy, Rex Is Not Your Lawyer, about a Chicago attorney with panic attacks.
"There's precedent to suggest that it won't crumble without me," Tennant said wryly. "Of course, it's slightly galling, but, no, I'm glad. Because I'm a fan of the show, I grew up watching it, so I don't want to be the man who kills it."
So other than himself, who's Tennant's favorite Doctor?
"It's a bit like a chick hatching from an egg, isn't it?" he said. "I think the one you first experience, if you fall in love with the show, you fall in love with that Doctor. So that would've been Tom Baker (1974-81) for me, as it would be for many. I mean, he did it for seven years, so he has a certain place in the history of the show. And then Peter Davison (1981-84), I suppose — the two of them were the two" he watched.
Davison made a brief appearance in Tennant's Doctor Who.
"Peter came and did a little sequence with us, which was fantastic. And that was very odd, for someone who'd grown up watching him, to then be in my TARDIS with him, visiting, in the costume. That was a very peculiar, very exciting moment for me."
The 11th Doctor, played by Matt Smith, 27, will debut in Doctor Who: The End of Time, Part Two, which premieres Jan. 2 on BBC America.
He might find Tennant a tough act to follow.
Tennant demurred when asked about a 2006 readers poll in Doctor Who magazine that named him the "best Doctor," but after four years in the role, the actor, who succeeded Christopher Eccleston in 2005, has clearly left his mark on the character, whose stay in Tennant's body has been marked by humor, manic energy and a certain sadness.
"I think what Russell has done — and it's partly because of the time he's writing it and the culture he's writing in, and also because he's a fantastic writer, who can do all the fancy action-adventure stuff but also has to get the characters a background and a full life — with the Doctor, he's examined what it would mean to be 900-odd years old and what it would mean to be the last of your people," Tennant said. "You really feel the genuine effect of that."