Romana I

The White Guardian originally assigned Romana to assist the Doctor during the quest for the Key to Time, which was a series of linked serials which constituted the whole of Season 16 (1978-79). Romana first appeared in The Ribos Operation, and was intended to be a contrast to the savage Leela, her predecessor. Romana was initially played as haughty and somewhat arrogant, looking down upon the Doctor (whom she considered to be her academic inferior) and responding to his initial resentment at her presence with icy put-downs. However, she soon gained an appreciation for the Doctor's experience and sense of adventure, and began to respect him as a teacher.

Over the course of Season 16, Romana appeared to take some of the characteristics of the screaming "damsel in distress", much to the annoyance of the actress who played her. When Tamm decided not to return to the role, Romana regenerated into Romana II at the start of Season 17, emerging with a different physical appearance and a lighter personality.

The suddenness of the regeneration scene was also dictated by real life events. Although Tamm had left the show on relatively good terms and did not object to returning for a brief regeneration scene, by the start of Season 17, she was very visibly pregnant, making her return impractical.