I loved all the efforts John Nathan-Turner put into Doctor Who when he became the producer, but some of his ideas were a bit questionable. John Nathan-Turner also was able to keep the show running until 1989, so he did everything he could to keep it alive. One thing he did though, was create the character of Tegan. He made the decision to have Tegan as a bossy Australian, with a high-strung personality. The story goes that Janet fit that bossy Australian personality, and so she came in and auditioned. She got the part, and so Tegan was created. The original idea was that Tegan may or may not stick around, after helping the Doctor through his regeneration. But Nyssa was originally a one off character, and was going to depart, and through the insistence of Peter Davison, Sarah Sutton stayed. It was then decided Matthew Waterhouse would be the one to go. The introduction to Tegan was actually well done in Logopolis. She is about to start her new career, when she and her Aunt Vanessa get a flat tire and stop on the side of the road. Mistaking the TARDIS as a police call box, Tegan opens the door and walks in slowly. Her Aunt has an encounter with the Master, and well, the result was not pretty. So here we have Tegan in the TARDIS, not even aware of what has happened to her Aunt until much later on Logopolis. When the Fourth Doctor tells her what has happened to her Aunt, he pats her on the shoulder and realizes he has to deal with the situation at hand. Tegan decides to stay with him on Logopolis and help him while the Doctor had strongly told Nyssa, Tegan and Adric to stay aboard the TARDIS. Now seeing Tegan is with people she doesn't know, the only assurance she has of getting home safely is by the Doctor himself. So of course she wants to stick by him. She feels he is the only one that will get her back to Heathrow. It makes sense. As a human being, she certainly shows a whole bunch of human emotions, although I don't agree with Turner's view that Tegan should have anger and bossiness thrown together all at once. Considering all the things Tegan had seen before she made the decision to stay on the TARDIS, it's amazing she didn't go insane. She'd been taken to another planet, she'd met the Master, she saw the Doctor regenerate into a younger man, and had the Mara take over her mind. Those are just a few things. True, some other companions may have handled it better, but Tegan handled it far better than what could have been done. It was the fact she only wanted to return home after making sure the Doctor recovered, and the Doctor kept failing to get her home, that made her angry. She had every right to be so.