"I was gonna be with you forever."
The Doctor first meets feisty young bride-to-be Donna Noble when she appears his TARDIS just after he's said goodbye to Rose. She comes across as brash, loud-mouthed and extremely strongly opinionated, and is at first reluctant to stay in the TARDIS at all - all she wants to do is get married. As she and the Doctor uncover an ancient alien plot, however, she decides to stick by him, especially as he keeps saving her life.
Donna is a very typical human being, and walks away from the TARDIS with a much broader mindset. The Doctor invites her to travel with him but she declines, admitting that she could never immerse herself in his dangerous lifestyle.
It doesn't take long for Donna to regret her decision, and she soon sets out to find the Doctor again, researching UFO sightings and conspiracy theories on the internet in an attempt to track him down. After reading up on Adipose Industries, she infiltrates the company, posing as a health and safety inspector. At the same time, the Doctor is also undercover there, and after a series of near misses, they eventually spot each other spying through opposite windows. After stopping Miss Foster's plans to turn the whole of London into walking blobs of fat, Donna finally joins the Doctor in his travels through time and space.
Donna is bolshy and confident, and is never afraid to put the Doctor in his place when he gets a little too 'spaceman' for her liking. Throughout her time in the TARDIS, she has been present at the destruction of Pompeii, solved a murder mystery alongside Agatha Christie, and fought against living shadows in the biggest Library in the universe.
Whilst on the Chino planet of ShanShen, a fortune teller forces Donna to take a right turning instead of left on the day she got her job at H.C Clements. In doing so, she never even met the Doctor, and he was subsequently killed beneath the Thames. On this new world, Donna agrees to accompany Rose to the UNIT headquarters, where she sees the TARDIS for the first time and discovers that the thing on her back that has been plaguing her for the last few years is, in fact, a time beetle. It was the beetle that made her turn right instead of left, and as a result a parallel world was created around her. Donna travels back in time and changes the car's direction by stepping out in front of a truck, causing her past self to turn left instead of right to avoid the ensuing traffic jam.
When the Daleks steal the Earth, Donna is left trapped inside the TARDIS, which is taken to the heart of the Dalek flagship, the Crucible, to be destroyed. By touching the Doctor's severed hand in a jar, a whole new half-human Doctor is born, and, after being electrocuted by Davros, the Time Lord intelligence from the meta-crisis is awakened inside Donna's mind and she uses it to help save the world and destroy the Daleks.
The Doctor is ultimately forced to wipe the Time Lord essence from Donna's mind as it would eventually kill her, and as a result she loses all of her memories of the Doctor and is taken back home to continue living an ordinary life as a temp, never nowing the potential she has.
When the Doctor sees Donna again, she is is engaged to be married to a man named Shaun Temple. Struggling to get by on minimum wage, the Doctor travels to their wedding day and presents Wilf with a present to give to her - the winning lottery ticket for that week's triple rollover, which he bought with a pound given to him in the past by Donna's father, Geoff Noble.