Rose Marion Tyler was the first known companion of the ninth incarnation of the Doctor, and also the first companion of the tenth incarnation. She was sealed off in a parallel world, before returning to her own, only to ultimately be returned to the parallel world by the Doctor, along with another version of himself. She shared a close romantic relationship with both the Ninth and Tenth Doctors, eventually living out the rest of her life in the parallel universe with the duplicate Tenth Doctor.
Rose was a sweet, gentle and sympathetic young woman, quick to adapt despite being thrown into strange events. She had her mother's acerbic wit and was not hesitant to use it. She fell easily into the role of the Doctor's latest companion and was brave facing various alien threats. She cared deeply about the Doctor, although she originally denied any sexual or romantic feelings towards him despite indications to the contrary. In what seemed their final meeting on the beach, she told the Doctor that she loved him; he began to reply, but only got out the words "Rose Tyler" before he was cut off.
However, besides Jack Harkness and River Song , she was the only recent companion of the Doctor's willing to kill the Doctor's enemies. Others, such as Martha Jones and Donna Noble were much more reluctant and Donna only killed once when it was the only way to save Agatha Christie. Rose was willing to call the Doctor out when he was wrong. When the Doctor brushed aside the danger that Jackie was in when faced with a Slitheen, Rose reminded him the woman he was discussing was her mother. She was horrified the Doctor would allow the Gelth to use human corpses as a vessel for their consciousness. The Doctor's failure to listen to Rose's human plea of respect for their dead led to at least two deaths when the Gelth proved to be malicious.
Rose had a jealous streak when it came to the Doctor. She and the Doctor's former companion, Sarah Jane Smith, traded barbs over who was the "best companion" but they became good friends afterwards, and happily greeted each other at their reunion on the Crucible. Rose was willing to sacrifice herself for the Doctor or the common good. When faced with the choice of dying or saving the world, Rose instructed the Doctor to do what he had to do to save everyone else. This was a common theme in Rose's story; despite the risk of plunging into the Void and an eternity of nothingness, she let go of a magnetic hold to set a lever right and seal the Cybermen and Daleks away from her world. It was only the sudden appearance of her father from the parallel world that saved her from that fate, but ultimately led to her separation from the Doctor.
