[4][5] Within the series' narrative, Donna begins as an outspoken Londoner in her mid-30s, a temp worker from Chiswick whose view of the universe is small in scope.

The scene was kept a secret until broadcast, filmed with minimal crew, and was a humorous postscript to the sad farewell the Doctor shared with companion Rose (Billie Piper) moments prior.

Donna is a temporary secretary at HC Clements in London, a security firm which, unbeknownst to her, is a front organisation for the alien-investigating Torchwood Institute.

[9] In the series four opener "Partners in Crime" (2008), two years later, Donna has become dissatisfied with regular life and more interested in the bigger picture after her father died.

When both are investigating the alien connection to Adipose Industries' Miss Foster (Sarah Lancashire), she and the Doctor are reunited, and she joins him in the TARDIS as a regular companion.

[15] In finale episodes "The Stolen Earth" and "Journey's End", Donna touches the Doctor's energised severed hand and is imbued with the totality of his knowledge, with which she is able to stop Davros (Julian Bleach) and his plan to destroy reality.

Early in the story, she buys her grandfather a book written by the episode's villain, which the Doctor takes to mean that the "DoctorDonna" is still trying to subconsciously lend a hand.

Following the ensuing chaos, the TARDIS strands the Doctor and Donna on a spaceship on the edge of the known universe in "Wild Blue Yonder".

They are tormented by two shapeshifting creatures who impersonate them, and the Doctor almost leaves Donna to die aboard the exploding spacecraft after mistaking her for her doppelgänger.

They battle with the Toymaker (Neil Patrick Harris), an old nemesis of the Doctor, who forces him to bi-generate, creating his fifteenth incarnation (Ncuti Gatwa) in co-existence with his fourteenth self.

Donna also appears in three original audiobooks published by BBC Books: Pest Control (May 2008), The Forever Trap (October 2008) and The Nemonite Invasion (February 2009).

[19] As indicated by David Tennant in his series two video diary (included in the DVD box set), the casting of Catherine Tate was kept secret; her scene in "Doomsday" was filmed with minimal crew.

[20] Executive Producer Russell T Davies at one time dismissed Donna's potential as an ongoing companion due to her abrasive personality, saying that "she'd get on your nerves".

Donna did not appear in his original conception of reunion episode "The Stolen Earth", despite planned reappearances from Martha, Captain Jack (Barrowman), Sarah Jane (Sladen), Rose (Piper), Jackie Tyler (Camille Coduri), as well as Mickey Smith (Noel Clarke), Elton Pope from series 2 episode "Love & Monsters", and the cast of spin-off series Torchwood.

[21] Davies originally intended the series four companion to be "Penny", a Northern woman with whom the Doctor would share a romantic attraction.

"[24] Ben Rawson-Jones attributes success to the natural progression of her character, her boisterous personality being toned down for her first 2008 appearance, "Partners in Crime".

[25] Who can ever forget the sheer visual hilarity of her silent first encounter with The Doctor in 'Partners In Crime', or her attempts to blend in to the deliciously Cluedo-esque world in 'The Unicorn And The Wasp'?

Digital Spy noted that fans initially worried about Tate's full-time casting, as she is known for her role as a comedian and comic actor.