CHARACTER NAME: The Master
CHARACTER SERIES: Doctor Who
SPECIES: Time Lord
AGE: ~900 years old. Appears ~40.
CANON POINT: Post End of Time.
NOTE: The Master's body is perpetually in a state of dying that I don't want the dragons to fix because I'm an awful person ;) He should be able to manage it without it ever killing him, which I state below!
The Master, having no real special powers beforehand, is going to have his “potential” unlocked in the form of a Warlock. He's one of those crazy people who thinks he can control the demons he summons and use them to do his dirty work while he stands back and laughs. His soul is already blackened enough, so he'll fit right into the usual archetype; however, he'll have a very hard time with the abilities. For every spell he uses, it expends a chunk of his own life force, just as everything else he does. Luckily, he'll get a kick out of draining peoples' souls/life to sustain himself. So what if it's not ethical. Ethics are for chumps that want to die. He probably won't be able successfully summon anything other than the imp for a very long time.
Other than that, he used to have a knack for hypnotism in previous regenerations, but it seems like he's either lost that ability in this body, or he stopped caring. He does, however, have a bit of latent physic ability that really only comes into play around other Time Lords (for example, he can sort of “sense” the existence of other Time Lords), but it does mean that he has very strong psychic defenses around his own mind, though they might weaken randomly due to the instability of his mental state. On a similar Time Lord note, he's able to sense Time... which... doesn't say a whole lot, really, and I don't imagine it'll work much in Azeroth, aside from potentially realizing that Azeroth's just gotten... weird when it comes to time, and even then I doubt it.
He technically is supposed to regenerate into a new body when he dies, but Azeroth's method of resurrection will just... circumvent that. Otherwise god, that would be awful, eh?
http://tardis.wikia.com/wiki/The_Master And because that link is massive, here's an... attempt to summarize:
The Master has existed, with a few periods of death, for over nine hundred years. He's spent most of that time being the counterpoint to his childhood friend, the Doctor. Two sides of the same coin, the Master was the villain, and the Doctor was the “hero.” This relationship lasted until the Time War engulfed their homeworld, Gallifrey. The Master was resurrected to fight, but ended up hightailing it in fear, running to the end of the universe and turning himself human. Cue another long strip of time where the Doctor was sure that this time the Master really was deader than dead, until his tenth self came across a man named Professor Yana. This man did not have his memories of being the Master; in fact, those memories were locked up nice and tight in a fob watch, and only unleashed when the Doctor's human companion at the time, Martha Jones, prompted him.
Yeah. Probably not the best idea. But hey! It meant that the Master was finally himself again, not some disgusting human, and after regenerating courtesy of his assistant shooting him, he got to steal the Doctor's TARDIS and go back to evil schemes, just like the old days!
He almost won, this time. He controlled Earth for an entire year until the Doctor and his companions ruined everything, and reset time. He nearly even had to put up with the Doctor, trapped, for the rest of his miserable life, but his “darling” wife shot him, and the Master, knowing that he had a backup plan in place, chose death over regenerating.
Unfortunately for him, that same “darling” wife is the reason that his resurrection went sour. Clearly that marriage was a mistake. His life goes downhill from there. Not only is his body broken, but he looks like his old role as the Prime Minister of Britain, and even after he tries to dye his hair and change his overall appearance, he's still recognizable, and he also has the Doctor to deal with. Lucky for him, an opportunity practically falls into his hands: crazy family with a side order of alien technology, which he is perfectly happy to lend his expertise towards. This, of course, translates into subterfuge and good ol' fashioned sabotage.
Long story short, the Master uses the tech to rewrite the biology of every single human on the planet, making them all him. Now he's got six billion Masters with an irksome drumming signal in their heads that they can triangulate and find the source. Which happens to be the Time Lords. The Time Lords who, apparently, ruined his entire existence by planting the signal in his head as a child, making him out to be insane, all so they could try to “save” themselves from the Time War.
Thanks Rassilon, you're such a nice guy.
Rassilon also thought a good way to “survive” was to ascend and collapse all of Time. He wasn't even kind enough to bring the Master with him, ruling the Master to be a disease, “albeit a disease of our own making.” Swell. The only way for the Doctor to fix this problem seems to be either kill the Master (because the signal is inside his head), or to kill Rassilon. The Doctor goes for Option C, destroying the device that the Master used to create a pathway. The Master in turn cobbles together some scraps of redemption, after lifetimes of fighting the Doctor, to instead save him from Rassilon, attacking the Lord President in his anger for what he did to his life, and ultimately ending back on the war-torn Gallifrey.
He's not there for very long. Before Gallifrey ends up frozen in a pocket dimension, the Burning Legion arrive.
And then he's pulled away to Azeroth.
Talk about a lot of travel whiplash.
The Master is a frayed being. Once stable and in control of his life, he's lost a lot of his control through a botched resurrection. He used to believe that he could change the whole of the universe and reshape it into his image, and that he would be the Master of All. Though his priorities have shifted, he still has an underlying desire to rule the universe, and it's because of that that he would rather fight the Burning Legion, rather than try to join them (if such a thing was even possible). He doesn't take kindly to their idea of “consuming the universe.” Being in Azeroth is actually a benefit to him; he has a strong thirst for chaos and disorder, but he had lost a proper outlet for it since the last place he was had been his home planet, Gallifrey, which was being torn apart by a different war before the Burning Legion got there.
So the Master is alright with playing soldier, especially if it means he's got some new power to have fun with. But the Master isn't highly invested with the sanctity of Azeroth itself. He doesn't care for the people, he doesn't care who he destroys on the battlefield, except perhaps the Doctor, and that is a twisted relationship. The Master has always been obsessed with the Doctor; the Rani, in their early pre-war lives pointed this out, and it has been revealed through his actions time and time again. The Master has at least once purposefully pulled the Doctor to a place of his plots. Everything the Master does, even now, is a show. A game. Even in a war-torn world, he intends to add flourishes and drama to his actions; what fun is it, otherwise?
But his body is in a constant state of death. He cannot hold onto his own life force, expending it in every action he does, whether it be a spell or if his emotions run haywire. Normally, he would have to eat a feast to keep his personal energy up. However, because he will be a Warlock, he will make use of Drain Soul (or Drain Life, depending what era of spells we're using). He might not kill people completely with it; more often than not, he'll take pieces from people, but ultimately he knows that this is war, and he wants to survive no matter the cost.
Survival has always been a desire of the Master's. Throughout the series, he's always found some way to return. But in this broken state of his, he's much more volatile than he used to be, lashing out sometimes on borderline hysteria as he tries to hold his body together. He'll continually keep trying to hoard power so that he can stand above those around him, especially if he ends up as a dragonsworn to a flight that he doesn't respect. His alliance is only to himself. He has no problem changing allegiance to whoever he thinks has the better advantage in a situation, especially when his survival is in question, and it could happen multiple times in the same moment.
Arguably, he's insane. It's not his fault, exactly. The Time Lords essentially “created” him, and then outright abandoned him. There was a sound of four beats (the “heartbeat of a Time Lord” or the drumming, as the Master refers to it) that was implanted in his mind when he was a child, and it stayed with him all his life, getting worse the closer he came to the instant in time when the High Council of Time Lords would put their plan into action. Though as viewers we have no way to know for sure, it's likely that the Master still possesses the drumming in his head. He's a loose cannon, able to change mood in the blink of an eye, but he is able to sometimes find enough peace in himself that he can do what is necessary; likely he'll be most in control of himself when he's on the battlefield, whether it be leading, running solo ops, or simply fighting.
Despite all his issues, the Master really is quite intelligent. He is definitely someone that falls under the category in believing that knowledge is power. As a Time Lord, he has lived a very long time, and decently retains hundreds of years of information, and he'll continue to gather information whenever he has the chance about the different races of Azeroth, the planet itself, and the other new soldiers brought from various worlds. He'll especially look for the weaknesses of others so that he can exploit them if he ever sees the need. He gets a bit of a thrill manipulating people, after all.
The only bright point in the Master's whole dark existence is that he stopped Rassilon from killing the Doctor. It's not enough to redeem his soul, or set him down a new, better route for himself. He's not entirely sure where he stands with the Doctor now, but they're still likely better considered as “best enemies” rather than ever being friends.