Christy

Name: Christy Johnston
Age 17
Home Planet: Earth
Home Time: 4132
Doctor(s) travelled with: The Tenth Doctor (One off), The Eleventh Doctor (Non-Canonical Eleventh Doctor)

Biography:
Christy was born on Earth near Exeter in 4115. Her father made devices for a multi billion credit corporation. Eventually, he created a serum to be used to enhance miltary performance. Her brother took the serum and turned into a monster referred to as "The Ultimo Creature". He killed their Mother and Father, and began to hunt Christy.

She then met the Tenth Doctor. He helped her by setting her brother free from being that creature, though it killed him. However, before her brother died, he stabbed the Doctor in the stomach. Christy took him back to the TARDIS and he regenerated. He then invited her to come with him.

She often expressed a fondness for his choice of colour in his attire of olive green. However, she was not a big fan of the Sherlock Holmes' style suit, but he wouldn't stop wearing it. During their travels together, she met Vampires, Daleks, Cybermen and The Master.

However, as people say all good things must come to an end, and her travels with the Doctor did. She took a shot from the Master's Temporal Disruptor protecting the Doctor and it erased her from time and space. Only the Doctor, the Master and Captain Jack had any memory of her existence. This affected the Doctor for some time and he refused to take any one with him for a time because of it.

Notes
Christy was the first companion of the Eleventh Doctor out of 3.
The thirteenth Doctor references her several times to Dani, even going as far as to compare the two on more than one ocassion, which is ironic as the Master killed Dani, albeit briefly, as well.
She is referenced directly by a delusional thirteenth Doctor when he is still regenerating as he thinks Rose Tyler's lodger is her.
The Doctor mentions knowing how her life would go if she hadn't been killed, and mentions she would have lived to have three children, two boys and a girl, and be happily married and head of Torchwood in London.
When the eleventh Doctor is still regenerating, she influences some of the changes to his personality, even going as far as his mannerisms where he picked up her excessive use of "We are in deep, boiling water."
When the Eleventh Doctor is regenerating, he believes her to be Rose Tyler and asks her to forgive him for leaving her behind in the paralel world with that "copy".