Roy Mustang is a state alchemist and officer in the Amestrian state military. A hero of the Ishval Civil War and Edward Elric’s superior officer, Mustang is a remarkably capable commander who plans to become the next Führer of Amestris. Mustang is a clean-shaven young man with dark eyes. His dark hair is casually unkempt, falling over his eyes; in more formal or somber situations, however, he is known to wear it neatly slicked back. A great fan of classy attire, Mustang is rarely seen out of uniform (and even while in uniform will often don other accouterments, such as a long, black overcoat and white formal-wear gloves), but when dressed in civilian clothes, he appears rather partial to the three-piece suit and black tie (frequently coupled with classic scarves, polished dress shoes, and the aforementioned overcoat and gloves). He tends toward dark or neutral colors in his dress, such as dark blue, brown, and black tempered with minimal white.

Spoiler

After the events of his fight with Lust, Mustang carries a faint scar on the back of his right hand in the shape of the flame alchemy transmutation circle. He also carries a large burn wound on his left side, lower back, and abdomen from the same event.

On the surface, Mustang is presented as a shallow, self-absorbed, and incorrigible womanizer who is infamous among many of his colleagues and subordinates alike for the selfish and narcissistic aura he gives off. Easily as arrogant as Edward Elric, Mustang is one to act ostentatiously and appears to act mostly out of self-interest rather than any sort of philanthropy. He comes off to most as a sort of cocky layabout, shirking most of his duties and delegating his paperwork to subordinates while sitting idly at his desk with an amused smile on his face as he procrastinates, but is quick to take action when it appears that there is glory and military notoriety to be gained. Mustang is expertly manipulative and prone to think several steps ahead of those around him, giving him a remarkable talent for making subordinates act exactly as he wishes despite appearing not to have had a hand in their decisions - all traits which make the fact that he has managed to attain the lofty rank of colonel at such a young age a matter of public gossip. Mustang also has a reputation of being a shameless flirt, and it's rumored that he spends much of his time cavorting about town with various women and wooing several of the servicewomen with his abundant charm, good looks, and charisma. This adds another facet to his unpopularity among the enlisted men, many of whom fear having sweethearts and crushes romanced away from them by his hand. He has, however, never actually been shown to be on a serious date with any woman; any flirtatious interactions he had with women seemed to be nothing more than a cover to discretely pass along information. At the core, Mustang is a remarkably devoted commander whose primary focus and personal duty is to his friends and subordinates. Though he hides it well behind a veil of cynicism and self-importance, Mustang is a man who cares deeply about the people who trust and support him and goes to great lengths to ensure their safety and well-being, even at the risk of his own. As a man with considerable power, Mustang considers himself a protector to those without and acts accordingly, earning the staunch loyalty of his most trusted compatriots. Orphaned at a young age, Mustang was adopted by his father's younger sister, who brought him up intending to make him into a fine gentleman. Presumably, in his teens, he discovered an affinity for alchemy and took basic instruction in the craft from master alchemist Berthold Hawkeye in the hopes of becoming a source of strength and knowledge for the people of Amestris. However, faced with the increasing frequency of border wars, he left his teacher's charge and enrolled in the state military academy with the intent of becoming a state alchemist and devoting himself to the protection of citizens caught in the crossfire of international struggles. While at the military academy, he became friends with fellow cadet Maes Hughes, with whom he often discussed his idealistic dreams for the future of the country.

Spoiler

Pride uses the Gold-Toothed Doctor to open the Gate of Truth, forcing Mustang into it. What happens while Mustang is at the gate is unclear, but as he leaves, he is transported to the room where Edward Elric, Alphonse Elric, and Izumi Curtis were taken before. Elric tries to talk to him, and Mustang replies that he cannot see; Truth has taken his sight as the price of looking inside the gate, either to "deprive the man who had a grand vision to save his country from his eyesight, denying him to see what his beloved nation will become". as Homunculus claims it to be, or merely to give a price for seeing the Truth. Mustang's blindness is later cured with a Philosopher's Stone at the end of the series. In Brotherhood, the stone is used to heal Havoc's paralysis before curing his blindness.

(Source: Fullmetal Alchemist Wiki, edited)