Tegan is twenty-one, an attractive and intelligent Australian trainee air stewardess, whose brash confidence in her own abilities actually conceals inner insecurity, a state of affairs that becomes clear in moments of stress.
On her way to her first real flight she accidentally blunders into the TARDIS and thus finds herself being inadvertently abducted by the Doctor. Characteristically her inner bewilderment at the new situation in which she finds herself causes her to assume an attitude of overweening self-assertion, and she begins to take charge of the Doctor and Adric.
During the course of three stories, Tegan's superficial self-assurance will build until it becomes a real problem for the other two occupants of the TARDIS, and it will need drastic action on the part of the Doctor to put things to rights and show her the error of her ways. She may or may not continue with the Doctor thereafter.
BBC Character Outline. John Nathan-Turner and Christopher H. Bidmead. 1 August 1980.