Expanded Personality and Abilities... because I am CLEARLY insane
Personality:
At first glance, Roy comes across as a polite but manipulative, arrogant and shallow womanizer who prefers to ride atop the crest of a wave propelled by the hard work of those beneath him instead of doing anything himself, but the first glance is only what he projects to those he doesn't necessarily want close to him, providing those around him with the most superficial view of who and what he is. Those who actually put forth the effort to get to know him will find that there's a lot more to him than that... because good god, there HAS to be more to him than "DOGS AND MINISKIRTS~".
Possessed of a keen intellect, a stubborn streak a mile long, a fierce determination, and a lot of confidence in both his abilities and his subordinates, Roy is a far cry from that first glance. He's charismatic, not arrogant -though he isn't the sort that everyone and their brother swoons over as evidenced by Olivier Armstrong’s attitude toward him- and while he's prone to procrastination, he's never without some sort of work-related task, whether it's for the military or his own information circles. That said, he's incredibly secretive and while he's polite in his speech and mannerisms, he has a tendency to speak cryptically at times and nothing is ever really what it seems with him. He's also rather temperamental as well as immensely protective of and loyal to those close to him. Roy doesn't have much of a family (the only relative that's ever mentioned is his aunt/foster mother) so his unit is his family and messing with any of them means one will have to deal with him.
While he is capable of manipulating others, it’s not necessarily something he does unless circumstances warrant it. He didn't have to manipulate Riza, Havoc, Fuery, Breda, Falman, or the Eastern Army into following him, they do it because they want to -they see something in him that strikes a chord with their own personal beliefs and feelings. He may manipulate situations to his favor or nudge others into doing what he wants them to by systematically chipping away at their other options and making his into the only logical course of action, but he doesn't take the credit for it; they're guided into coming to the conclusion that they decided on their actions and paths themselves.
Because of his methods, new people and situations are regarded with caution until he's able to get a feel for them, which in turn causes him to come across as somewhat cold. He's a rather private person where his own life is concerned, and he's been raised to be polite yet cautious since one never knows who is or isn't in your corner. Everything and everyone is taken with a grain of salt and a degree of suspicion until he can clearly ascertain that there is nothing to be wary of. If one can control the circumstances, then one can, in theory, control the outcome and that is the reason for which he takes great pains in assessing both the situation and the individual.
Roy is generally popular with the women of East City, both young and old alike and has been said to have received as many as 203 love letters (many of which lead to dates and according to Havoc, he works fast with a letter in the morning and a date that evening), earning him a reputation as a womanizer, but in reality his 'dates' are primarily informants and his reputation is a carefully crafted front to keep outsiders from looking too deep. His research notes are also part of this ruse, all of them encoded using the names of women and written as though it's a recap of his various dating exploits. In fact, he's even gone so far as to give the men of his unit female codenames so that when they're out of the office, they can relay information back to him under the guise of his chatting it up with one of the girls. Case in point is when Riza requested a leave and he granted it, only to turn around and spend his time talking to Elizabeth on the phone -to anyone in the office, it sounded as though Riza was what kept him in line, when in truth it was Riza on the other end. Because of his dual role as military commander and part of a vast information network, he doesn't have much time for activities outside work since even when he isn’t in the office, he's still on the job.
Due to said dual role, he not only doesn't have much time for outside activities, but it doesn't afford him much time for sleep either. When he isn't in uniform, he's usually out with informants or playing the womanizer, and so because his time is stretched so thin, he's infamous for catnapping around the office (the Resources Room is one of his usual haunts for a powernap). It helps to deceive his superiors because they're less inclined to believe that he's capable of doing much beyond riding the wave of his subordinates’ work into his next promotion. If they keep their perceptions of him rather low, it allows him the ability to move more freely as he isn't being constantly watched and having his movements restricted. He tends to put his paperwork off until the last minute, but whether it's because it's part of the front or because he just really hates paperwork is never given much attention. Personally, I don’t see him as the sort to enjoy paperwork very much.
His biggest motivator/goal/dream/whathaveyou, basically that which governs his entire life, is his love for his people, his country, his home. To this end, nothing Roy has really done in his life was for the sake of himself; everything was done for the sake of others. According to what he told Riza as they stood at her father's grave, In this profession, you never know when you'll wind up dead in a ditch somewhere, like a piece of garbage, but if I can help strengthen the foundation of this country and protect its people with my hands... that would make me happy.
He joined the military in order to use his life to protect the people of his country. He learned alchemy in order to better serve those people. Hughes’ suggestion of climbing to the top struck a chord with him because there was no better place from where the people could be protected than that. He allowed his own public movements to be restricted in order to keep Riza safe while she was a hostage of the Fuhrer. He takes action knowing that he could be incarcerated or executed for his choices, but so long as the people are protected, he’s content. Every one of his actions, every step he takes, every dream he has involves some sort of sacrifice or potential sacrifice on his part. So long as the people are safe, so long as his loved ones are safe, whatever becomes of him is of no consequence.
As he told Hughes after the war in Ishbal, If one person can only do so much, then I want to protect as many people as possible. Even if it's only a few, I want to protect those who matter to me. Those below me will in turn protect those below them. Human beings are weak, but they should be able to accomplish that much at least.
The biggest problem with his mindset, though, is that his closest subordinates see him as someone important, the sort of man the country needs, and as such they're more than willing to help him in any way possible, even if it's at the expense of their own safety... which, in turn, only causes him to rush headlong into danger in order to protect them. It's like a Circle of Protection in which the one doing the protecting is the one the protected wants to protect.
Another aspect to his personality, one that isn't stated outright but is inferred through his actions, character profile books, and manga-ka interviews is that Roy is neither materialistic nor goes out of his way to be noticed in his appearance, instead allowing his demeanor and presence to speak for him. He doesn't wear flashy clothes, preferring to stick to neutral and subdued colors such as blacks, browns, grays, and whites when not in uniform, and his hair is usually a bit disheveled unless it's a formal occasion, then it's slicked back neatly. He also isn't one to be caught half-dressed as he has a burn scar that wraps around the lower left side of his body from the center of his stomach to the middle of his back from where he cauterized his own injuries after the encounter with Lust (to give an idea of the severity, he insisted Havoc was done rare while he was medium). As for materialism, it's stated that what he owns amounts to his clothes, his car, and his couch... and that's about it. The house he lives in is rented and from the way he drops money to informants, he doesn't leave himself with much more than what he needs to live on.
There is one thing, though, that he does his best not to show to those he isn’t close to -as in those who aren’t within his “inner circle”- and that is the fact that despite his intelligence, his caution, his idealism, his ambition, his talents, and his secrecy, Roy Mustang is a dork. As an alchemist, he falls under the banner of “alchemy geek”, but he pushes that envelope just a little further due to the fact that Flame Alchemy requires a strong understanding of the Periodic Table in general and the manipulation of explosive and flammable gasses in particular. Dealing with gasses, he would have to understand the way that the molecules combine in order to separate them while at the same time knowing what not to do and which not to touch in order to avoid blowing himself and everyone around him sky high. He’s also rather childish in his antics at times, from a long rant endorsing canine slavery to the way he picks at Major General Armstrong like a kid poking a sleeping lion with a stick, and his actions don’t always come across as terribly mature -such as his snarky responses to Edward and his enjoyment at sending out false Scar reports. His sense of humor is also a little… off, as evidenced by his inability to make a convincing joke when bringing up the Fuhrer’s homunculus nature to General Raven.
Abilities - Strengths:
Given that Roy enlisted in the military prior to his becoming a State Alchemist1, it's safe to say that he has undergone basic combat training. This would include the ability to fire a gun properly and accurately although he isn’t quite Riza’s caliber, basic first aid, and basic hand-to-hand combat skills, but his preference -as well as his most notable ability- is alchemy.
Being a State Alchemist, Roy has a knowledge in the overall basics of alchemy and has stated that while he has a general knowledge in medical alchemy, it isn’t his specialty2. This means that while he is capable of using it, his knowledge in that field is rudimentary at best. In fact, Dr. Knox even scolded him on his sloppy transmutation of the Dummy!Ross, though fortunately all it had to be was passable since it was intended to be charred.3
His specialty is Flame Alchemy, but in truth, it's actually the ability to adjust the oxygen levels in the air by decomposing the carbon dioxide molecules into carbon and oxygen via the array on the back of his gloves.4 He does carry scars on the back of his right hand in the shape of his array from the encounter with Lust5, but he has never tried using them after they healed over. By manipulating the oxygen in the air, Roy is able to direct the path of the flames as well as their intensity. He doesn't create the flames at all, instead relying on an outside source for the spark to ignite the adjusted oxygen; this spark typically comes from the gloves he wears, which are made from a special type of cloth quite possibly consisting of fibers woven with flint (or a type of ferrocerium) and steel, but anything that would create a spark can be substituted. Dubbed "ignition cloth", the spark is produced through the friction created by rubbing his fingers together -hence the snapping gesture. The 'snap' sound itself comes from the spark igniting the oxygen and not from his fingers6, as anyone who's tried to snap their fingers in a pair of gloves knows that it's almost impossible to get that sound.
Another thing to note is that Roy is capable of producing both large explosions and small, pinpoint blasts, but not both with the same hand. Possibly due to a difference in manual dexterity, the larger explosions come entirely from his right hand while the smaller pinpoint blasts are purely done with the left*. This prevents him from being limited to the position of a long-range fighter as he can use the smaller bursts for enemies that are "too close for comfort" where a larger explosion would be suicide.7 For anything else, he carries a handgun concealed beneath his clothes, in a holster under the jacket.8
He also tends to use his alchemy as a means of scoring a date with women who don’t fall under the label of ‘informant’. By adjusting the oxygen levels around his intended target, he waits until they grow dizzy then swoops in to catch them before they fall, asking if they alright then following it up with an invite for tea.9
His determination and drive. Come hell or high water, if there is something he's set his sights on, one can bet he will fight tooth and nail for it. From his goal of becoming Fuhrer10 to his desire to ensure that Hughes' murderer was caught11, he won't let anything stop him from seeing it through, even if he has to make a few detours and a do a little backtracking along the way.
His overall intelligence. Roy tends to try and keep several steps ahead of the game, whether it’s planning for every conceivable outcome or keeping many a backup plan in reserve.12 He’s also fairly decent at improvisation for when none of his backup plans fit the situation.
Roy's greatest strength is his friends. They provide him with the strength to go on just as he does for them, and because of his willingness to lay down his own life for them, they're willing to reciprocate in turn. Through them, his goals have been given new life13, shaped14, and strengthened to the point where they withstand even the most trying of times15-16. So long as they are by his side, even if they’re scattered across the country, he is able to keep going despite obstacles.
Abilities - Weaknesses:
He is 100% human17 despite the nicknames given to State Alchemists, and thus susceptible to any number of human ailments from jealousy to anger to illness to injury to death.
For all intents and purposes, water in general and the rain in particular adds up to one big ball of useless Colonel. Roy's specialty is Flame Alchemy, and with wet gloves and no outside source, he has no means of generating the spark, thus his skill is rendered impotent18. With an outside source, though, rain is revealed to be his biggest "weakness", as water's molecular construction is H2O. On dry days, Roy uses his alchemy to break down the carbon dioxide (CO2), but carbon isn't a flammable gas and won't ignite in air, so controlling the blast only requires adjusting the concentration of oxygen. In the rain, however, splitting the molecules is dangerous because both hydrogen and oxygen are present, and both are incredibly flammable. Therefore, using his alchemy in the rain poses a major risk to everyone in the surrounding area as the blast would be far more difficult to control... because for every oxygen molecule he splits, there are two hydrogen, and hydrogen ignites in air when there is a concentration present between 4-74%19 so if he were to ignite the oxygen, the hydrogen would explode and cause far more damage than the detonation of the oxygen alone. Hence why he is “useless” on rainy days. He’s perfectly content with that… though he does forget himself sometimes when provoked and has to be forcibly reminded of his “uselessness”.
While he keeps several backup plans on reserve, he’s not quick to ask for outside help unless he’s backed into a corner20, but he has to realize he’s in that corner before he can ask. The longer he’s kept in the dark about his own position, the less likely it is that he can make that call and get backup.
What is quite possibly his greatest weakness is also his greatest strength: his friends. Roy is immensely protective of those that he calls "friend". They are his family, his companions, his allies, his supporters, and without them, he has nothing at all. He knows this, so he goes out of his way to ensure their protection, to the point of putting his own life on the line if it means they remain safe. When they're in danger, he doesn't hesitate to throw caution to the wind and rush headlong into the front lines for them.21 The death of one of his own, however, leaves him with a terrible drive for revenge that can often leave him blind to reason and rationality.22
1 Viz media. FullMetal Alchemist Vol. 15, Ch. 58, pg. 7-11.
2 Viz media. FullMetal Alchemist Vol. 10, Ch. 38, pg. 51.
3 Viz media. FullMetal Alchemist Vol. 11, Ch. 42, pg. 33.
4 Viz media. FullMetal Alchemist Vol. 10, Ch. 38, pg. 45.
5 Viz media. FullMetal Alchemist Vol. 10, Ch. 39, pg. 87.
6 Viz media. FullMetal Alchemist Vol. 2, Ch. 5, pg. 7.
* Viz media. FullMetal Alchemist (assorted volumes, gleaned through observation)
7 Viz media. FullMetal Alchemist Vol. 23, Ch. 94, pg. 122-123.
8 Viz media. FullMetal Alchemist Vol. 8, Ch. 31, pg. 55-62. (jacket) / Vol. 2, Ch. 7, pg. 104. (hip).
9 FullMetal Alchemist: Book in Figure RED, Teach us! Riza-sensei!
10 Viz media. FullMetal Alchemist Vol. 3, Ch. 10, pg. 59.
11 Viz media. FullMetal Alchemist Vol. 8/10/14/23, Ch. 31/38/56/93, pg. 60/37/115/90.
12 Viz media. FullMetal Alchemist (CHECK SOURCE!)
13 Viz media. FullMetal Alchemist Vol. 15, Ch. 61, pg. 159-160.
14 Viz media. FullMetal Alchemist Vol. 15, Ch. 61, pg. 169-173.
15 Viz media. FullMetal Alchemist Vol. 16, Ch. 63, pg. 83-89.
16 Viz media. FullMetal Alchemist Vol. 21, Ch. 87, pg. 142-145.
17 Viz media. FullMetal Alchemist Vol. 14, Ch. 57, pg. 147.
18 Viz media. FullMetal Alchemist Vol. 2, Ch. 7, pg. 109.
19 Wikipedia "Hydrogen"
20 Viz media. FullMetal Alchemist (CHECK SOURCE!)
21 Viz media. FullMetal Alchemist Vol. 10, Ch. 38, pg. 24.
22 Viz media. FullMetal Alchemist Vol. 23, Ch. 93-95, pg. 89-94, 109-153.