Peter Capaldi made his debut as the new Doctor with a series of digs at his own expense.
Glasgow-born Capaldi is the 12th actor to play the Doctor in six decades of the Doctor Who series. At 56, he is also the oldest since the first, William Hartnell.
Doctor Who fans saw a new complex Doctor and there were differing reactions on Twitter to the first dose of this darker, more prickly Time Lord. Capaldi, perhaps best-known as a foul-mouthed spin doctor in The Thick Of It, has taken over from his 31-year-old predecessor Matt Smith.
As he spots different things about his new form, including his accent, Capaldi's Doctor announces "I am Scottish I have gone Scottish", which he says is good because "I can complain about things".
Although the Doctor has changed, his companion has not. Jenna Coleman returns as Clara Oswald, who was also Smith's sidekick.
At one point Clara also tells the new Doctor about his head of silver hair, saying: "If I got new hair and it was grey I would have a problem."
The episode - called Deep Breath - also includes a dinosaur, robots who are turning into men and talk of getting to the promised land.
Smith pops back for a small appearance in a telephone call to Clara and he asks her: "Please tell me I didn't get old - anything but old. I was young. Oh, is he grey?"
Some of the online reactions included Alex Hunt who said: "Bit disappointing when your favourite part of a new episode with a new Doctor is when the old one calls in for a cameo... #doctorwho"
Amy Quinn tweeted that said she "cried" while watching it.
Paul Ilett described it as a " Great opener for #PeterCapaldi in #doctorwho - more character, more emotional depth. Feels like the show's back on track."
Samantha Jayne tweeted: ?"So impressed with that episode. Didn't feel like a kids show for once, it felt like a drama. Complex characters, awesome script. #doctorwho"
A peak of 7.3 million viewers tuned in to watch the feature-length opening episode of Doctor Who, the BBC said.
There was an average of 6.8 million viewers across the whole programme and the show attracted 33% of all viewers who were watching TV during that time slot.
The BBC said this made it the most watched series opener of Doctor Who since 2010 when Matt Smith took on the role.