The Carrick family was a canny and ruthless one, doing whatever it took to gain power and then keep it afterwards. Magic had always sprung up sporadically in their ranks and they encouraged its growth, but barring a few familial spells and traditions it was a very raw kind of talent they possessed, though not one that people wanted to cross, as they used it well.
When Rowena Ravenclaw first found the land where Hogwarts was meant to be, she and the other founders discovered that this land was, in fact, land that belonged to the Carricks. However, instead of fighting off these powerful witches and wizards, the Carricks welcomed them and invited them to build their school where they pleased, as the Carricks knew that it was through these witches and wizards that their might of magic would grow.
To further foster relations with the founders, the then Toísech Carrick ('Toísech' being the nearest equivalent to 'Baron') went so far as to invite Godric Gryffindor into his home to spar with him and practice his own magical talent. It is here that Godric met his eventual wife Alana, sister to Toísech Carrick.
When Aonghus was born, both Toísech Carrick and Godric were over the moon. Godric took the role of godfather (in addition to Uncle) to Aonghus and assured Toísech Carrick that Aonghus would have a place at Hogwarts.
When he was growing up, Aonghus loved to watch his father and Godric duel. While Godric would usually win between the pair of them, it was obvious that the two had great respect for one another, although they would often disagree about how things should be done in regards to ruling. Aonghus tried his very best to hone his skills as he watched and could even do bits of wandless magic when he focused, but he did not have the strength that Godric or his father did.
His father had wanted to start teaching him the moment he showed signs of magic, but it was Godric's belief that forcing magic to work beyond its capacity at too young an age would stunt its growth later, so his father respected that and taught him nothing of the old family magics at the time. When it was time for him to start learning, Godric himself took young Aonghus to the Ollivander clan, where Godric had gotten his own wand.
While he was thrilled that he was able to get into Hogwarts on his own merits, Aonghus was a little disappointed when he didn't make it into Godric's house. He soon found, though, that Salazar was a more than fine replacement. It was under Salazar's tutelage that Aonghus's canning flourished and Aonghus was always eager to prove himself worthy of Salazar's teachings. He would duel with other students with a ferocity unheard of and he soon was more than capable of holding his own against even Godric's students.
On those times when he did fall short, he would first go to Salazar for advice, since it was his house that he belonged to, but he was unafraid of going to Godric for advice if the need called for it. Godric was, at times, unsettled by the aggressiveness and rage of his nephew but he never gave up hope that such aggression and rage could be a proper asset to the young lad given a proper channel.
Aonghus was saddened when Salazar left for a few months but was surprised and pleased when Godric took the lead in teaching Salazar's students while he was away. Aonghus was further astonished when Godric kept to Salazar's style of learning, teaching the young Slytherins the art of being canny and ruthless, albeit through the lens that Godric saw the world. It was a bold and brash kind of canny, and Aonghus loved it.
When Salazar returned, his young wife Serena in tow, Aonghus and his other housemates were thrilled to death, and were even more so when Serena became pregnant. Aonghus would have rather that his teacher had married into his clan so that he'd gain another uncle, but he understood the desire Salazar had to marry a woman from his own country.
It was in his third year that he learned that Rowena Ravenclaw had a daughter of her own, and a radiant young lass she was. Helena had been raised by Rowena's family while she was up at Hogwarts because she, like Godric, did not think that teaching magic early was a good idea. However, Helena was a fast learner.
Aonghus was saddened but not surprised when Helena was sorted into Ravenclaw's house although he made a point of doing his best to befriend her, on the outside because having such a brilliant family marry into his clan would be a boon for his children, but inside because she resisted him and attracted him, making him feel odd and happy all in one go.
Serena Slytherin gave birth to a daughter, Madelena, in Aonghus's fifth year and a son, Diego, in his sixth, which pleased his father greatly, as his father felt that if Madelena married Aonghus when she was old enough it would be quite the coup for the family, though Aonghus quietly disagreed, having eyes only for Helena.
In his last year at Hogwarts Aonghus's father became sick and Aonghus began to spend more and more time with him, learning the old family magics that would give Aonghus an edge over the other witches and wizards that he'd been learning with. Aonghus had, at this point, mixed feelings about keeping magic secret from his fellow students, but was more driven by a desire to be able to dominate them, so he kept them quiet.
It was this magic that allowed him to dominate Peeves, a poltergeist that had manifested when enough young witches and wizards had begun to live in Hogwarts' halls. Peeves had, prior to this, not listened or cared what anyone else thought so Aonghus's hold disturbed Peeves to his core, and thereafter Peeves was careful to not bother Aonghhus and did as asked so long as it was within reason.
When Aonghus graduated from Hogwarts, such as it was, he went to take charge of his clan almost immediately, as his father had taken a turn for the worst. It was not long before he passed, and Aonghus became the new Toísech Carrick. He reaffirmed his father's approval of Hogwarts and went even further, inviting wizarding families from all over to come live near the new school, dubbing the new wizarding community 'Hogsmeade' in honor of the school. He did not take a leadership role in the community, although his word would often pass for law there because of his role as the Toísech Carrick as well as his temper, which had not gotten better with age.
As Madelena grew older, it became more and more obvious that both Salazar and Serena approved of the idea of her marrying Aonghus. Madelena herself grew in grace and loveliness as time went on, but still Aonghus had eyes only for Helena. Helena herself was by now utterly repulsed by Aonghus and would tell him as much on many occasions, but this only spurred him onward. When Helena stole her mother's diadem and ran away, Aonghus leapt at the opportunity to go and retrieve her when Rowena asked him to, setting his uncle Godric in charge of the clan while he was away as he had no siblings.
Like a dog after a scent, it took Aonghus relatively little time to find Helena, considering that she had hidden herself away across Europe in deep forests, using as powerful magics as she could summon to hide herself. When he found her, she refused to return and threw insult after insult at him, verbally (if not magically) cursing Hogwarts, her mother, and finally him.
It is unknown as to why these insults were what tipped him over the edge, as they were similar to all others she had thrown at him, but he flew into a rage and slaughtered Helena were she stood.
When he came back to himself, he was horrified and killed himself as well in shame. This would do him no good, though, as he found that even death did not release him from his remorse. He eventually found his way back to Hogwarts. There, everything was almost thrown on its head. Helga Hufflepuff was the last founder to remain at the school, as Salazar had fled in a rage, Godric had died in a duel and Rowena had died of a broken heart. He wandered the halls listlessly until he found himself back in his old house, and there he took up the role of the Slytherin House Ghost.
He's had a few favorites over years and has even taught them some of his family magic if he liked them enough. He despised Voldemort and the attitude he cultivated in Slytherin house, refusing to show him anything but rage and hate. It was not due to Voldemort's parentage that he hated him, but because of how the young man saw the world and generally viewed Voldemort as the final corruption of the first dream that Salazar Slytherin had for Hogwarts.
