Ushas, better known as the Rani and known more formally as Ushas of Miasimia Goria, or, in other accounts, as simply Rani, was a renegade Time Lady and member of the Deca. A brilliant but cold neurochemist, she knew the Doctor and the Master when all three were young, and became an enemy of the former and an unwilling ally of the latter.
The Rani's incarnations
The Rani was, regardless of incarnation, a brilliant scientific genius whose villainy came not from the usual variety of lust for power and suchlike, but from a mindset that treated everything (including morality) as secondary to her research. She was highly intelligent but extremely arrogant, narcissistic, ruthless, powerful and intensely cruel.
The First Rani was a cruel woman whose evil deeds and notoriety had made her the second most wanted criminal in the galaxy, after the Master. (AUDIO: Requiem for the Rocket Men) Much like the Doctor, she had a considerable presence. This presence, however, rested not in a fondness for the planet but as a focal point for her research projects. (TV: The Mark of the Rani, Time and the Rani)
Just as amoral as her previous incarnation, the Second Rani always believed that the end always justified the means. Not above making jokes at the expense of others, she held a great disdain and disinterest in the Doctor's antics. Unlike her previous incarnation, she had a certain level of anxiety in breaking the Laws of Time. (AUDIO: The Rani Elite)
In the War in Heaven, the Lord President reintegrated several barely-reformed renegades into Gallifreyan society. One former renegade Time Lady, who was known for her engineered creatures, became a tutor to newly-loomed soldiers. Holsred remembered a lecture in which she connected an artron energy generator to a white rat's brain and then let the rat use the energy to kill a hungry Gallifreyan cat. (PROSE: The Taking of Planet 5)
Behind the scenes
Return to television
Following her last live-action appearance in the controversial TV special, Dimensions in Time, the possibility of the return of the Rani in the post-2005 revival of Doctor Who has become a subject of widespread fan speculation, as the preeminent renegade Time Lord antagonist in the "classic" series aside from the Master, who made his return in Series 3. The matter was discussed or joked about on several occasions by the showrunner.
Russell T. Davies once stated that if he had brought back the Rani, he would have cast actress Ruthie Henshall in the role. In the commentary for Last of the Time Lords, Davies jokingly termed the hand seen removing the Master's ring from the ashes of his funeral pyre "the hand of the Rani". He would later write it being the hand of a human Disciple of Saxon in The End of Time. In a email reprinted to Benjamin Cook reprinted in Doctor Who: The Writer's Tale - The Final Chapter, Davies choosing to deliberately leave the identity of the Woman (in the same story, The End of Time) ambiguous, anticipated that fans might believe her to be, amongst other possibilities, "even the Rani", "but of course it's meant to be the Doctor's mother".
Me & My Ghost, a 2021 Dionus's War audio play written and produced by Bill Baggs, featured a character called "Nari", who was an alternative personality crafted for herself by an infamous renegade of the Great Houses to evade the authorities of her people. She was noted as a talented chemist, and it was suggested that the name "Nari" was somehow a play on her usual appellation. The clear implication was thus that Nari's true self was "the Rani". However, this was not made explicit due to BBV Productions no longer having the rights to the character of the Rani by that point, aside from further exploitation of their original licensed The Rani Reaps the Whirlwind spin-off story.