Romana (Romanadvoratrelundar) was the Doctor's companion from The Ribos Operation to Warriors Gate.
Romana I[]
The White Guardian originally assigns Romana to assist the Doctor during the quest for the Key to Time, a series of linked serials which constitute the whole of Season 16. Romana first appears in The Ribos Operation, and was intended as a contrast to her predecessor, the savage, Leela. Romana is initially haughty and somewhat arrogant, looking down on the Doctor (whom she considers to be her academic inferior) and responding to his initial resentment at her presence with icy put-downs. However, she soon gains an appreciation for the Doctor's experience and sense of adventure, and begins to respect him as a teacher.
Over the course of Season 16, Romana begins to take some of the characteristics of the screaming "damsel in distress", which reinforced Tamm's decision not to remain in the role as she felt the character had been taken as far as she could go. As a result, Romana regenerates at the start of Season 17, emerging with a different physical appearance and a lighter personality.
Although Tamm had left the show on relatively good terms, and was willing to film a regeneration sequence for the start of Season 17, she was not invited to do so.
Romana II[]
The introduction of Romana's second incarnation in Destiny of the Daleks, a script credited to Terry Nation, but with several additions and alterations by script editor Douglas Adams, treats the concept of regeneration humorously. At the beginning of the serial, Romana changes bodily forms several times, rather like someone casually trying on different outfits, before deciding to take the form of Princess Astra, who had been played by Lalla Ward in the final serial of Season 16, The Armageddon Factor. This regeneration scene is controversial with some fans; see "Romana's Regeneration".
Romana II enjoys a more intimate relationship with the Doctor than her predecessor, to the point that some fans have assumed a romantic relationship with the Doctor. Although a relationship was never explicitly shown or intended by the writers, many fans have found the signs of a romantic relationship particularly evident in the story City of Death, perhaps reflecting the real-life romance between Tom Baker and Lalla Ward which blossomed during the production of that story, leading to their brief marriage. In many ways, she is the companion most alike her Doctor - besides being of the same race and comparable intelligence, she occasionally mimics his sense of style, wields her own sonic screwdriver and can occasionally get the better of him in moments of banter and more practical situations. As her practical experience develops, she also becomes more assured and capable in the situations she encounters.
Her final television appearance was in Warriors' Gate, where, along with the robot dog K-9, she leaves to forge her own path in the parallel universe of E-space when faced with a choice of remaining there or returning to Gallifrey. She also appears briefly in the 20th Anniversary special The Five Doctors through the reuse of footage from the uncompleted story Shada.
After the departure of both Romana I and II, both versions of the character also appeared very briefly in flashback sequences during the Fourth Doctor's regeneration in Logopolis as well as the Fifth Doctor's mind-copy in Resurrection of the Daleks.
She would also be mentioned in Castrovalva during the Fifth Doctor's post-regenerative confusion, as well as Arc of Infinity, where the Fifth Doctor, in response to a reprimand from the High Council of Time Lords for "leaving [her] behind", retorts that she "chose to remain in E-Space".
Ward also appears in a brief cameo as Romana in the 1993 charity special Dimensions in Time.
In "The End of the World", the Ninth Doctor stated that his homeworld had been destroyed and that he was the last of the Time Lords. Whether Romana was killed with the others has not been specifically established on screen. Of note, while various spin-off material reveals Romana later became President of Gallifrey after returning from E-Space, this is clearly not the case at the end of the Time War, in which the Time Lord founder, Rassilon, is alive again and claiming the title.