2. Romana
The regal Time Lady Romanadvoratreludar became the Doctor's companion under unusual circumstances. She believed that the Lord President himself had requested her to assist the Doctor in the quest for the Key to Time when it was actually the White Guardian. The Doctor initially resented having Romana foisted upon him; her formal demeanor and strict adherence to the rules clashed fiercely with his cheerful attitude and carefree methods. In time, however, Romana began to relax and enjoy the adventurous side of their travels, and she learned more from the Doctor than she ever had at the Time Lord Academy. The Time Lords eventually took notice of her actions and ordered her to return to Gallifrey, but having tasted the freedom the Doctor enjoyed, Romana was reluctant to go back to the stuffy strictures of Time Lord society. Fortunately for her, her final adventure with the Doctor provided her with a legitimate excuse to avoid returning to Gallifrey. During the time they spent in E-Space, they encountered a time-sensitive race known as the Tharils, who were often enslaved and exploited for their powers. Romana realized that the Tharils needed outside assistance if they were to gain their freedom, so she made a very matter-of-fact decision to stay behind and help them. Although it is generally assumed that she returned to N-Space and Gallifrey to assist in fighting the Time War some accounts state she even served as the President before Rassilon reappeared we know little about her stay with the Tharils. Was she able to help them? And did she manage to survive the Time War? If she did, where is she now? The Doctor once stated that if there were other Time Lord survivors, he would be able to telepathically sense their presence. So perhaps if Romana did survive, she used the chameleon arch to disguise herself much like the Master did.