Abby


 * You may be looking for any of a number of individuals named Amy.

Amy, later Abby, was a tracer in human form. She traveled with the Doctor as his companion during his second search of the Key to Time.

Biography
Amy, short for Amethyst, like her "twin sister" Zara existed to find the different segments to the Key to Time. When she first met the Doctor, she was just a few minutes old, and recruited his help in tracking the six pieces of the Key to Time, making her the first companion who makes the Doctor her companion. (BFA: The Key 2 Time - The Judgement of Isskar)

Her travels with the Doctor turned her into a human being, one with a strong sense of right and wrong. She became a very clever and resourceful young woman, for example saving the life of Romana whilst Zara and the Guardians would have her converted into the final segment of the Key. After the Key was destroyed by the Doctor, Amy was invited by Romana to Gallifrey to join the the Academy in order to become a Time Lady. (BFA: The Key 2 Time - The Chaos Pool)

Amy later followed Zara to a place called the Sphere where Zara tried to bring her back to Pargrave, a soldier that Zara had fell in love with. Amy then changed her name to Abby in order to infiltrate the Sphere and find Zara only to find out a major secret from her sister. Zara had fallen pregnant to a man called Marek. He had become Zara's protector and taught Zara and Abby about the Sphere. Abby and Zara were unable to teleport out of the Sphere. They used their powers to earn enough money to escape from the Sphere. (GRC: The Sphere)

Abby and Zara eventually escaped The Sphere only to find more trouble. Abby and her sister found themselves in a villge, called Compton, in 1912 that was surrounded by a mysterious fog, and whose citizens believed the women had killed their loved ones by making them vanish into thin air. The tracer twins are then taken into custody. Both make and attempt to escape but only Abby succeeds. Abby found herself slightly outside of village only a week into the future and that the village has been destroyed. (GRC: The Fog)

Behind the scenes

 * Amy's name was changed to Abby for the Graceless series. Though the in-universe reason for this development has not been revealed, it was likely that the change was made to avoid a correlation with Amy Pond.