I think that like the Doctor, many of the Master’s incarnations have been reactions to their previous incarnations. Delgado not so much—I mean obviously we don’t even know what his previous incarnation was like, but I also think at this point he’s just casually going through life, trying his hand at this and that and having a laugh. While he definitely commits himself 100% to each of his plans, he’s also not taking any of it that seriously. I don’t think he truly grasps the consequences of anything he does, because he’s never really had to deal with them.
Crispy, meanwhile, although he was once an ordinary Master, is primarily defined by his unfortunate circumstances—the consequences of his previous lives finally catching up with him. His desperate quest to survive (and to make everyone else suffer as much as he has) is what shapes him. He becomes very bitter and serious and pragmatic by necessity—he can no longer afford to just have fun with his schemes. He has to ensure they succeed, because his survival often depends on them. He does take joy in some of them, but even then he tends to be more reserved about it.
Ainley, of course, is the opposite—once the Master gets a new body, he reacts against his previous dour persona and has as much fun as he possibly can. His schemes become far less practical and far more theatrical. He has the freedom to dabble in convoluted rule-the-universe plots and mess with the Doctor all he wants, because he’s no longer a barely-animated skeleton. I think deep down though, he knows that his time is still limited in this weaker, non-Time Lord body, and that ultimately catches up with him in Survival, where a very different side of his persona is revealed—one much closer to his decaying self.
His life goes back to a constant struggle to survive after that, and in the end—as Roberts—he finally fails and, in his bitterness, chooses death over accepting the Doctor’s help.
When he’s resurrected by the Time Lords, and finally given a new Time Lord body, he goes back to enjoying himself and being as outrageous as possible, though with perhaps a harder edge than before.
His timeline between Macqueen and Yana isn’t entirely clear yet (we’ll know more about Jacobi once his audios come out, and the Titan Comics stuff complicates it all further if you want to count them as canon—which I’m actually quite happy to do because they’re good), but it seems Macqueen’s exuberance has faded somewhat by the time Jacobi comes along. The universe is a different place now, with the Time War breaking out, and the drums beating in his head. Instead of choosing to fight, the Master ultimately goes back into survival mode and hides from the consequences as usual.
Simm is a pretty clear reaction against the Yana persona the Master had been living as for so long (as well as a reaction to the Tenth Doctor). He may not be free of the drums, but he’s free of the Time War and can be himself again, which means rebelling against everything that was good and kind and gentle about Yana. He’s crueler than ever before, and delights in using that cruelty to get reactions out of people. As with Ainley, the joie de vivre is back as well, though Simm backs it up with more successful schemes.
The interesting thing about Simm is that he usually gets what he wants—control of the Earth, humiliation of the Doctor, resurrection, bringing back Gallifrey, horrifically mutilating the Doctor’s friends, a way off the colony ship—he gets it all. But he never gets to keep it because ultimately everyone always rebels against him. His life is proof that fear, manipulation, and coercion don’t work in the long run.
That’s not a lesson the Master learns easily though, since their whole thing is control. And when Simm’s schemes are working, they work really well. He leaves Gallifrey after The End of Time in probably the best state he’s been in since Delgado. He has a TARDIS, a Time Lord body with many regenerations left to go, there’s no Time War looming on the horizon, and the drums are finally gone. I imagine he probably travels for awhile in peak arrogance mode, causing as much casual destruction and chaos as he can before eventually getting stuck on the Mondasian colony ship. And then, like the Doctor says, he killed a lot of people, took over the city, lived like a king until they rebelled against his cruelty, and is forced into hiding—because as with all his other schemes, hurting people comes back to hurt him in the end. He deliberately drives away everyone who cares about him—the Doctor, Lucy, Bill, and even his future self. And even when this clearly results in his own downfall, his refusal to change is so adamant that he shoots Missy so he can have the final say. If any final proof was needed of how self-destructive the Master’s choices had become, this was it.
All of this, of course, shapes who Missy is, even if she doesn’t remember much of it. She realises she has to do things differently, and decides she wants to rebuild her relationship with the Doctor. But of course she doesn’t want to change herself to do that—she wants to change him. She needs him to admit that her methods were right all along. So she gets him an army. Perhaps, despite Simm’s claim that he didn’t listen, she remembers some of the Doctor’s speech in The Doctor Falls. “I do what I do because it’s right.” / “Armies are for people who think they’re right.” / “If I run away today, good people will die. If I stand and fight, some of them might live.” / “All those people suffering in the Dalek camps? Now you can save them. All those bad guys winning all the wars? Go and get the good guys back!”
If he wants to fight for what’s right, she’ll give him an army to fight with. The catch is that by accepting it, he’s admitting that violence is the answer. He’s admitting he’s no better than she is—and if he can admit that, then what reason does he have to reject her? They can be friends again.
It doesn’t work, of course, and that failure marks the Master’s last big evil scheme. In their next encounter, she tries a more subtle approach—mostly helping the Doctor, but then trying to manipulate him into killing Clara.
When this too fails and the Master finds herself once more caught up in consequences—this time in the form of yet another execution—it’s not entirely surprising that she might finally start to realise her methods… don’t actually get results. Of course, I don’t think she has any real intention of changing when she’s begging the Doctor for her life—she’ll say pretty much anything he wants to hear if it’ll keep her alive—but at this point it’s also pretty much the one thing she hasn’t tried yet. And once the deal is made and she’s put in the vault, maybe she thinks, “What’s there to lose?” Every other choice she’s made has backfired in the end, so maybe it’s time to try something new. She’ll give being good a go, if only to prove that it doesn’t work either.
The tragic thing is that in the end, it almost does work. When the Doctor gives his speech, she finally gets what it’s about—she realises that sometimes there are more important things than simply ensuring one’s own survival. And for perhaps the first time, she admits the Doctor is the one who’s right. This is huge, because the one thing the Master has been willing to die for in the past rather than give up is their own high ground—their own sense of ideological superiority over the Doctor.
And of course, predictably, Simm chooses death for both of them to maintain that superiority.
I still… really want to see more of this story. Because while I’ll continue to think the Master’s storyline wasn’t integrated into TDF as well as it could’ve been, my issues with the unsatisfyingness of this ending will go away once it stops being an ending. I mean, it’s not that it doesn’t work as both redemption and poetic justice for the character, it’s just that I hate redemption storylines that don’t actually follow through on a character’s development after they decide to change. I always want to see what happens next once they make that big choice rather than just watch them go out in a blaze of glory (or die without hope/witness/reward in Missy’s case).
Ideally, I want to Missy herself back so we can see where she goes from here, but if we can’t have that I’d be equally interested to see what kind reaction her next incarnation would be to these events. Would they take her development further, or would they turn away from it? There’s so much I want to see explored, but I suspect we’ll probably have to wait quite some time before it happens.