Expanded Background
Regulus' childhood was a mostly pleasant one, full of warm memories of growing up in the family home at 12 Grimmauld Place in London. He wanted for little, and enjoyed spending hours playing with his siblings, at least until they went off to Hogwarts School of Witchcraft and Wizardry. First his brother, then his sister. It was not until 1917, two years after Lycoris went off to Hogwarts, that Regulus was finally able to attend. In truth, it is perhaps because of this immense sense of waiting that accompanied much of his early years, that he views his life as not really beginning until it was finally his time to receive a message by Owl, informing him that he had been accepted to attend. And so, with brand new, magnificent robes, a new owl, and his own new wand, he set off to become a true Wizard.
Hogwarts was truly a magnificent experience for Regulus. He was of course sorted into Slytherin House, as was expected. But more then that, he made friends near instantly, not just within his House, but with others of his age, and even older. As the years passed, it became clear that where Regulus was not naturally gifted or blessed, he worked hard to make up for the lack, so that there were plenty that thought him perfect. Indeed, he was very popular, and attracted friends and followers with seeming effortlessness. He eventually made the Slytherin Quidditch Team, and when the time came, he was chosen as Prefect for his House. His scores on his OWLs, and later his NEWTs, were above reproach. Truly, the only thing it can be said that Regulus did not have was the title of Head Boy. Yet for all that, in his last year, he might as well have had the title, for the way the student body regarded him.
Yet with such things, there is always a cost. For Regulus, there were three prices above all others that touched him and changed him, even if he did not let others see.
The first cost was the expectations that others had for him, most of all his parents. There was a reason that he was so driven. He was a Black. He was expected to excel at everything he put his mind to, to have everything that he wanted, everything that his parents wanted, and then still strive for more. And for every victory, for all the pride that his parents expressed to him, there was always something held back. Always an underlying meaning that he somehow could have done better, should have. More then this, there was the expectations of his friends and peers, and even his teachers. If sometimes he displayed a casual disregard for other people, and a confidence in himself, he still cared deeply and often secretly felt wanting. He did not so much care about what they thought of him, but about being worthy of their praise and attention, and in also giving back as much as he could. He always felt there was more that he could do, on all those counts. And if it was these morals that often leaked through his public demeanor and drew people to him, it was also this that worked him to the breaking point throughout his years at Hogwarts, not just pushing himself till the point of exhaustion, but in making it all seem effortless when he was held up to the light of day.
The second cost was something slowly revealed to him, yet keenly felt. For though he was popular, or rather because of it, more and more Regulus began to feel alone. He was admired and liked by most, yet his efforts and the persona he showed the world, the pedastle that he had placed himself on, meant that he never truly connected with people. He had many friends, and later many girlfriends, yet noone that truly understood him. It is a wound that he bore silently, never showing anyone, and it has since scarred over and effected his relationships to this day.
The third and final cost was perhaps unexpected, at least for Regulus. For though he always felt like he had more to achieve, he never truly doubted that he could. He simply had to push himself hard enough, far enough. Work more, and longer. It was not until his last years at Hogwarts that this confidence nearly threatened his very sanity - for though it gave him so much, allowed him to do so much, when he eventually failed his nearly impossible standards, it changed his life.
For nearly the entirety of his education at Hogwarts, Regulus seemed to float through it all on gilded wings, at least to the public eye. He always kept a good face on things, even when feeling like he might fall over from exhaustion. So it is that no one really knows just how bad things got, at the end. It was little things at first. First it was failing to get the position of Head Boy, which he could tell dismayed his parents. Then it was how after six previous years of increasing amounts of sleepless nights and exhaustion, his body and mind both finally started to give under the ever increasing pressures, and his perfect grades turned into merely exceptional, and then finally simply noteworthy. Then there was how his Quidditch Team, which he was then Captain of, failed to take the Cup in what would be his final year at Hogwarts and of playing that sport both.

The final straw though was that after the nearly perfect grades that he got on his OWLs, he set the impossible standard of getting an O on every NEWT when it came time to take them in his final year. And if he had taken only the courses he was passionate about, showed true talent in, such as Charms and Transfiguration, he likely would have succeeded. But, like many young witches and wizards, he wanted to be an Auror. And so he took the ones he struggled in as well, especially potions. And when, at the end of the year, he got an A in that subject, it meant a broken promise to himself, the first such grade he had ever gotten, and also the end of his dream to be an Auror.
Somehow, Regulus still managed to make it look so easy. He kept his head held high, he smiled to everyone, and he seemed to take it all in good stride. Yet inwardly, the cracks finally started to deepen and nearly threatened his grip on himself. He had been so certain of it that he had not tried to reach out to other prospective employments, so sure that the combined weight of his grades, skill, and family name would make him a sure thing for becoming an Auror. If he had been able to recover himself sooner, perhaps he would have attempted to become a Hit Wizard, and perhaps one day found a way to become an Auror regardless of that grade. But as it was, he felt a cloud of shame over his head when he returned home, and so let his parents decide what he would do next with his life.
It was in this way that after graduating, Regulus did indeed find himself working at the Ministry, if not in the capacity he had expected or wanted. For it had always been expected that he would serve in government, perhaps one day eventually rising as high as to take the reins of the Minister of Magic - in his own mind, it was a far off thing, and would have been long after he had retired from being an Auror, with many a dark witch or wizard having fallen to his wand. But now, here he was, working directly for the Minister of Magic… as a clerk. An assistant. A glorified fetch boy.
It was this indignity that eventually woke Regulus up from his stupor, and healed the cracks and scars that had formed with his previous realization that despite what everyone else thought, he was not perfect, and could not actually have everything he wanted. Because truly, this was an indignity for him, for all that the position promised an eventual rise very close to the seat of power. It was not what he wanted, what he felt what he deserved. And for all his new realization, another came to him. If he could not have everything he wanted, he would not simply give up trying on achieving what he wanted most. And that was to prove himself worthy to others, to make a name for himself, and to further excel that of the Noble and Most Ancient House of Black.
It was quite by accident that Regulus found his current calling, yet when it came, it fit him perfectly. It was a couple years after he had graduated, and while he was slowly attempting to reform himself, and find his new mission in life, it came knocking on his door, so to speak. In fact, the message came by Floo, and it was an emergency summons to the Ministry. The Minister's office was in a tizzy, running interference as a severe case of Ludicrosis (a magical disease that causes wizards to behave like hyperactive children on vodka-spiked Kool-Aid) broke containment at St. Mungo's, and the contagion reached the streets, infecting first dozens, and then hundreds of wizards. In the face of such calamity every able-bodied wizard and witch in the Department of Magical Accidents and Catastrophes scrambling to maintain the Statute of Secrecy, and in an effort to contain the situation while the Healers of St. Mungo's did what they do best, the Accidental Magic Reversal Squad was temporarily recruiting from suitable wizards and witches from nearly every available department.
And that, really, was it. Years of working himself to exhaustion put Regulus ahead of the game, so to speak, and he impressed his superiors with his ability to continue on with little sleep, and the masterful way he reversed spells without much effort. In this way, and in keeping a cool head in such a crisis, he impressed the senior witches and wizards of the AMRS. And more then that, Regulus realized he had found his calling, seeing nearly immediately the potential in it, as well as the feeling of 'rightness' that he got from finally being able to do something he felt worthwhile. Thusly, when the sickness was finally contained and everyone else went back to their normal positions, Regulus was easily able to pursue and obtain a position within the AMRS. In short order he had transferred, proceeded with his training, and soon enough he found himself within the ranks of the Accidental Magic Reversal Squad
It all seemed right to Regulus. His own personal philosophies, his abilities, his need to do something more then just paperwork… it fit. And though at first his parents, especially his father, were upset that he was throwing away the opportunity they had obtained for him, he eventually convinced them that it would not hinder their eventual ambitions for their son. After all, someone who could rise through the ranks of a department, especially one that dealt with crisis on a near daily basis AND dealt with the frustratingly chaotic lives of muggles on top of that would be earmarked for greater things. Such a wizard would show leadership qualifications that went beyond the ability to simply be a politician, but inspire trust and confidence in others - in essence, someone who could rise high within the Department of Magical Accidents and Catastrophes might well make a very suitable Minister of Magic, one day.
And so, that is where Regulus finds himself now. A rising star within both the Accidental Magic Reversal Squad, and within his Department as a whole, he inspires the same sort of trust and respect that he did at Hogwarts, if perhaps in a different way. And this time, he is more cautious in how he approaches his ambitions.