Kasgi

Kasgi was an expensive and highly competent assassin who chose to only accept targets who she deemed deserved death. On one occasion, she wrenched control of the Doctor's TARDIS from the Seventh Doctor and took on the name of "the Doctor". Although she went around claiming that she was in fact a regenerated form of the Time Lord, this was not merely impersonatin; Kasgi insisted that the Seventh Doctor acknowledge him as his successor, and claimed that he ought to be proud of what she was achieving in the name of the Doctor.

Hired by Ux
At some point prior to an intergalactic conference where a treaty for syncing the timelines of the Kollian Dimension with Gallifrey's universe was proposed, Kasgi was hired by Ux, a native of the Kollian Dimension. She was tasked with killing Prince Luj, leader of the Frovians, the main race who wanted to gain access to the Kollian Dimension. Though Luj claimed that his motives were purely peaceful, many Kollians including Ux rightly suspected him of actually wishing to gain access to the Kollian Dimension so that he could use his army to plunder it for its riches and enslave its people. (COMIC: Who's That Girl!)

Becoming the Doctor
Because Luj, in his friendly public persona, had nurtured a friendship with the Doctor, who was slated to make an appearance at the conference as Gallifrey's representative, Kasgi decided to become the Doctor. She managed to enter the TARDIS and tied the Seventh Doctor to the TARDIS control console using magnetic clamps, before putting together a Doctor outfit for herself. She materialised the TARDIS in the hall of Luj's castle on Okul just in time and greeted Luj as an old friend. Soon, she heard the grievances of the Kollians, and, within her charade, pretended she was hearing them for the first time; kneeling, she made a pledge on behalf of Gallifrey to keep an eye n the Frovians if the deal went through. When a dissatisfied Kollian tried assassinating Luj by themselves, Kasgi tackled them to the ground, saving Luj's life for the time being — she later explained that this was simply because she would not receive her payment if Luj died any other way than by her hand. (COMIC: Who's That Girl!)

A plan derailed
Getting into the persona of the Doctor, she returned to the TARDIS to demand that the "previous Doctor" acknowledge that she was doing well. The Seventh Doctor began to insult her for simply being an amoral assassin, prompting her to explain about her moral principles; the Doctor was shocked to learn that Luj had in fact been deceiving him all these years. As soon as Kasgi and Ux left for the hall to try again to assassinate Luj, he managed to escape. After verifying Kasgi and Ux's allegations for himself, he burst into the council room and officially declared that Gallifrey was withdrawing all support from the treaty or the Frovians. Losing all faith in the deal, the Kollian delegates who had been ready to sign tore the treaty apart as Luj called for revenge against the Doctor. (COMIC: Who's That Girl!)

Kasgi once more
When Ux looked round too tell Kasgi he would no longer be needing her services, he found that she had already disappeared. Having cast off her "Doctor" clothes and reverted to her old self, she watched unseen from a cornice as the Seventh Doctor returned to his TARDIS to leave. She felt pity for him about him having lost a friend in Luj, and also a grudging respect for the way in which he had defused the war without spilling any blood. However, her business instincts soon took over again and she began to wonder if Luj would be interested in hiring her to take a contract on the actual Doctor. (COMIC: Who's That Girl!)

Personality
Kasgi's calculating assassin side seemed to be at war with a more humane, moral streak in her personality. She took pride in her job and in being an "expensive" assassin, but only accepted contracts on people she believed deserved to be killed. Despite feeling pity and respect for the Seventh Doctor after their encounter, she did not hesitate for more than a moment to inquire with Luj whether Luj would like her to assassinate him. Kasgi seemed to either not realise or care about the more than immediate consequences of her action, preparing to assassinate Luj even though this would spark a war between the Frovians and Kollians just as surely as if she let Luj carry out his "evil plan". (COMIC: Who's That Girl!)

Abilities
Kasgi was an expert assassin. She could change outfits quickly and slip out of sight without anyone noticing. She had quick reflexes and was good in hand-to-hand combat, including non-lethally if the situation called for it. She proved cabale of flying the Doctor's TARDIS to Okul after she took control of it, although she was evidently unaware of some details of its construction, such as the electromagnet in the central console which proved vital to the Seventh Doctor's escape from the bonds with which she had shackled him. (COMIC: Who's That Girl!)

Appearance
Kasgi appeared as a tall blond woman with long, slightly wavy hair and full lips. In her normal occupation as an assassin, she wore a simple black catsuit. As the Doctor, she picked out a costume including high-heeled boots, light trousers with thin vertical stripes, a question mark jumper, a long striped scarf, a jacket, and a Panama hat similar to the Seventh Doctor. (COMIC: Who's That Girl!)