No this isn't an article about River Song! It's an article about the one other constant throughout the long history of Doctor Who other than the Doctor himself. What can it be?
It's the TARDIS! She was seen recently as Idris in an episode called The Doctor's Wife.
If anyone or anything should be the Doctor 's wife, it's his faithful time machine which has accompanied his adventuring throughout the show for so many years.
It's not often that the TARDIS herself has become central to the plots of the various stories throughout the show's run. The Doctor's Wife may have went one step further by actually giving us a TARDIS in human form, but it certainly isn't the first time that the TARDIS has been integral to the plot of a story.
The Doctor's desire to repair the TARDIS's Chameleon circuit by block transfer computation, is a leading plot line from Tom Baker's swansong Logopolis. In Colin Baker's Attack of the Cybermen, we finally get to see a fully functioning Chameleon circuit, as the TARDIS takes on various new forms. However at the close of this adventure the circuit has failed again and the ship once again becomes a Police Box.
At the end of the Second Doctor's adventure with The Faceless Ones, the Doctor's TARDIS is stolen from right under his nose and driven off in the back of a lorry. This leads us into the classic Dalek story - The Evil of the Daleks.
The Doctor obviously has a lot of affection and love for his faithful time machine, as witnessed by some emotional moments in the Matt Smith episode The Doctor's Wife. Even when he briefly becomes angry with her, it's still unmistakable of the high regard he has for the time machine. This story is just a little more emotionally charged simply because of the high dramatic performances from both Matt Smith and Suranne Jones.
The Doctor's TARDIS is a Type 40 TT capsule, planet of origin Gallifrey, in the former constellation of Kasterborous, before the Time War saw the planet and it's entire system laid waste. It's recently become known that although other Time Lords did survive the Time War, they unfortunately fell into the clutches of an evil entity. As the Doctor discovers to his disgust in The Doctor's Wife, he is able to reverse the damage the entity has done by taking over his TARDIS, by appropriating the soul of his TARDIS and downloading her into a human host. Despite getting to know his TARDIS through it's human persona, the Doctor still remains enraged that the soul of his ship has been violated in this manner.
More proof of the Doctor's enduring love for his ship, for as she has told us in human form, the Doctor calls her Sexy! But only when they're alone.
And indeed she is! Throughout her many different interior designs, different consoles and the beautiful Police Box exteriors. The TARDIS is as iconic as the Doctor himself, she truly is the Doctor's wife.