Joanna Harris was a human who became a vampire for most of her life, but later had her vampirisation undone, though this may have been temporary.
History
Joanna Harris was born in Canterbury, England in 1087 on the same day that William the Conqueror died.
About four hundred years after her turning, Harris was hit by what she would later dub the "Mid-Death Crisis", the point in an immortal's life where they feel that they have done and seen it all, and threaten to quite literally die of boredom. Unlike many vampires around her, Harris pulled through it, focusing on her drive to survive.
She worked many jobs over her life, including hairdresser and manicurist at a very expensive hotel, though after five years of perfecting this craft she grew weary of it and quit.
The leader of a vampire coven in San Francisco, Harris had, by the 20th century, taught herself rudimentary biology. From the safety of a job at Angel Labs, she was working on a substitute for blood that would no longer let vampires be reliant on their immoral hunting. In doing so she faced heavy opposition from her less scrupulous thralls, who thought her experiments were "trying to go against their nature". Unlike them, Harris found no joy in hunting, and believed that they only delighted in terrorizing mortals due to boredom (she, for her part, had "not been bored since they invented the Internet").
When the Eighth Doctor came to her and her vampires with a peace offering, proposing to help them research a blood substitute in exchange of which they would cease all attacks on humans, Harris, overjoyed at finding a more knowledgeable ally who shared her goal, agreed to pactise with him. As a token of trust between them, she had them partake in a bloodfasting, the first-ever (as far as she knew) between a mortal and a vampire rather than two vampires.
In the days that followed, the Doctor and Harris strengthened their bond not only physically but metaphorically, becoming fast friends — though neither trusted the other completely. A wedge was driven between them by the Doctor's discovery that Joanna had, in the months prior to their meeting, been feeding the depression of Dr David Shackle, in the hope that he would let her turn him into a vampire, and that he could thus act as her scientific assistant — as the Eighth Doctor could not abide Joanna's gambling with Shackle's life (since he was, by the Doctor's analysis, "as likely to just slit his wrists as to join [Joanna]"). They were further divided when the Doctor discovered that Harris's research into the food substitute hadn't focused on wholly synthetic blood as he'd assumed, but on breeding a "slave race" of mutated “humans” devoid of higher brain functions, which would make killing them for food "precisely as ethical as eating cows" — an endeavor which the Doctor found monstrous and inhumane.
However, she and the Doctor were once again allies when the Doctor's allies had their final showdown with Slake's rebellious vampires at the Opera. As the Doctor began to die from a grievous wound inflicted upon him by Slake, she attempted to turn him into a vampire himself in a last-ditch attempt to save his life, but was instead poisoned by the Vamp-Away he had drunk earlier in the hope that it would kill Slake if Slake dared to bite him. The Doctor, using their bloodfasting link, was able to keep her alive, but the Vamp-Away killed the V Factor within her, leaving her a mortal human.
Though all involved agreed it was better than nothing, Harris regretted her immortality greatly, mournfully telling the Doctor that "he'd killed her" when she realized what had had happened to her. However, he talked her into enjoying her newfound life and living as a human, with her keeping the option to later find another vampire to turn her all over again, if she still yearned for vampirism after a few years of it. She and the Doctor parted on good terms, and she went on to become a biology advisor for Adrienne Kramer's branch of UNIT. (PROSE: Vampire Science)
Physical appearance
Joanna Harris was a woman of average height with dark hair she usually kept in a ponytail. She was usually described as "slouched" and "disheveled", having long ago stopped to care much about her appearance. Being a vampire, Harris had their trademark fangs, though hers were "very subtle and unshowy", barely more than unusually sharp canines. (PROSE: Vampire Science)