Donna Noble was a companion of the Tenth Doctor. Despite her ordinary origins, she was noted by Rose Tyler and the Tenth Doctor as being the most important woman in all of creation. Donna saved the whole of reality from the Daleks and Davros, though to survive the stress caused by her transformation into the "DoctorDonna", her memories of her time with the Doctor were forcibly erased and she was returned to Earth. She later married Shaun Temple.
Donna's first encounter with the Doctor was bewildering for both: the Doctor was shocked into speechlessness by her sudden appearance in his TARDIS; Donna was furious with the Doctor for "kidnapping" her. Though Donna's sharp tongue and hair-trigger temper kept the Doctor at arm's length for most of their first adventure, quieter moments showed a more level-headed and perceptive woman. Although she sometimes appeared unintelligent, and persistently referred to the fact that she was 'only a temp', she was actually quite smart: she mastered the Dewey Decimal System in two days working at a library. When she joined the Doctor in his journeys, her quick, and sometimes dry, wit often came out, coinciding with his own.
Though most companions were, to some degree, the Doctor's conscience, Donna adopted this role more openly and forcefully than her predecessors. She pleaded with the Doctor to save the inhabitants of Pompeii - if not all of them, then a single family. Donna insisted that the Doctor acknowledge Jenny as his daughter, no matter how she was created or what job she was trained for. Donna's fiery temper hid a deep well of compassion, as she showed when she reached out to Agatha Christie, trying to share her own story of failed marriage.
When the Doctor's companion Martha Jones recalled the Doctor to Earth, she and Donna became fast friends; neither was jealous and both were willing to share experiences. The Doctor found this disconcerting. Her relationship with Rose Tyler was initially abrasive in the alternate timeline but friendly in the real universe. She also enjoyed an attraction to Captain Jack Harkness, which at one point involved her pushing Sarah Jane Smith out of the way to get a hug from him.
Unlike Rose and Martha, Donna was intent on maintaining a platonic relationship with the Doctor, reacting with disgust when she misinterpreted his comment "I just want a mate" (friend) as "I want to mate" (breed). She kissed him, but only to shock him. She was very supportive of the Doctor, at one point forcing him to admit that despite the potential collapse of universes, Rose's return was a good thing. She also supported the Doctor when the time came to leave the Meta-Crisis Doctor and Rose behind on Pete's World. Just before her memories were wiped, she tearfully echoed Rose's earlier desire to travel with the Doctor "forever". The Doctor reciprocated Donna's feelings, referring to her as his best friend. The Meta-Crisis Doctor, working from his original template's memories, recognised Donna's brash attitude arose because she truly believed that she was unimportant; she was "Shouting at the universe, because she thinks no one is listening." The original Doctor attributed this to her mother never telling Donna she was important to her.