The Doctor has a large number of recurring enemies: the Daleks, the Cybermen, the Nestenes, the various species of Silurians, to name but a few. All of them have changed over the course of their Doctor Who timeline from a production perspective, and their narratives certainly grow and adapt. You can read extensively on how all of the Daleks appearances fit together for example it is truly incredible stuff. It is not as though the Master's character is the only one responding to the Doctor's. And yes, much like a Cyberman, some things about the Master will remain far more immutable than the Doctor, an effort to be a good man is far greyer than it is to be an evil one. Nor, to be clear, is the Master particularly interesting due to his powers, or weapons, or plans to kill the Doctor, despite the efforts herein to shed light on their importance. Certainly, there are plenty of other madmen setting up brilliant, near admirable schemes for world domination, which require great cruelty. What the Master brings to the world of Doctor Who is two-fold. The Master is a rare true equal, perhaps the only true equal, for the Doctor. While the Doctor can admire the brilliance of an evil mastermind like John Lumic, or grow to appreciate the steadfast loyalty of his own human companions as he did with the likes of Jo Grant, and Rose Tyler, ultimately the Master impresses him in a way no one else can. They are not only renegade Time Lords, but renegade Time Lords with lifelong grandiose ambition. This binds them, couple that together with a history that stretches back even further than the Doctor and his TARDIS and arguably the relationship between the Doctor and the Master is the most important relationship in all of Doctor Who. In thinking about this relationship between the Doctor and the Master I come back to two quotations from Terror of the Autons. When asked why the Master is not angry about the Doctor having thwarted his plans, the Master responded: "He's an interesting adversary. I admire him in many ways." If there is one guiding light to writing a new Master it is in that line. In closing, these words from the Doctor. When asked whether was worried about coming up against the Master again, he said: "I'm not...I'm rather looking forward to it." Well, me too, Doctor. Me too.
A person who thought a lot, then decided thinking with other people is more fun. If you fancy a chat, feel free to email NicoleatWhatCulture@excite.com