Tegan Jovanka (Janet Felding) 1981-1984
Tegan appears in all but one of the Fifth Doctor's stories. She's an air hostess from Australia who often complains about the Doctor's inability to control the TARDIS, and has suffered considerable trauma on her journeys, being posessed by the entity known as the Mara at least twice.
Actually, Tegan didn't appear in TWO of the Fifth Doctor's stories: "Planet of Fire" and "The Caves of Androzani".
Otherwise, this primer is great!