Regulus Arcturus Black was born April 4, 1960 He was the son of Walburga and Orion Black, and younger brother to Sirius Black. With a family motto like Toujours pur (always pure) he was raised to believe that his family was far superior to others, but most especially to Muggles and Muggleborns. For Regulus this was not hard to believe, since he had only his parents’ word to go by and did not actually meet anyone that was not of pureblood descent until attending Hogwarts at age 11.
Regulus falls quite easily into doing what his family wished, as he was generally apathetic about things he determined to be "inconsequential" and "nothing more than politics". He also sought to beat his older brother, Sirius, in anything possible. Sirius was the rightful heir of the Black line, yet he hated his family and what they stood for. By taking over Sirius' role as the obedient child, he became his parents’ favorite by far. At home, if not at school, he was able to be the better liked Black. While he often resented Sirius for being more popular and better liked, Regulus also loved and respected him. With not much than a year' difference between them, they had grown up fairly close. Unfortunately, Sirius and Regulus had different opinions on their family beliefs. By the time Regulus turned 16, they were no longer speaking.
At Hogwarts he was easily sorted into Slytherin, as that was what his parents wished of him and therefore what he wanted for himself. He was, for the majority of the time, surrounded by people who thought like his parents. Regulus did have interactions with Muggleborn children, but if this bothered him he never showed it. Truthfully, it wasn't particularly something he cared about. He was spoiled, and arrogant. He truly believe that Slytherin was the superior House, and when asked; that his parents were correct in their beliefs.
Upon turning 16, Regulus was given the opportunity to make his parents truly pleased with him, and he took it. Without realizing what he was signing up for, Regulus received the Dark Mark. Before this all he had managed to do was parrot back what information his parents gave him without making up an opinion of his own. He soon came to realize that this was not as simple as being better than someone else and "putting them in their place." This was war.
After two years of servitude with the Death Eaters, Regulus was looking for a way out, and excuse, anything. He had lost what few friends he had that were not Death Eaters, he had lost what camaraderie he had with his brother, and he was afraid he was losing his soul. When Voldemort left Regulus' house elf (Kreacher) for dead, Regulus decided to act. He had been close enough to what was going on to find out what Voldemort was up to, and immediately set about to destroy the locket Horcrux. Knowing he was going to die, he left a note inside the fake locket for Voldemort to find, confessing to having stolen it. Regulus died afterwards, drowned by the Inferi Voldemort left to protect the locket. Regulus was only 18 years old.
Though Regulus was a spoiled and arrogant child, his final act of courage was also one of secrecy. No one knew how he died until many years later, nor that he had been the one to steal one of Voldemort's Horcruxes. Unfortunately, his death came too quickly for even reconciliation with his brother, who like many others believed he had been killed by Death Eaters.