Regulus Black

"Fight, fight for my master, the defender of the House elves. Fight for brave Regulus!"

- Kreacher

Regulus Arcturus Black (1961 - 1979), also known as R.A.B., was the son of Orion and Walburga Black and the younger brother of Sirius Black, Harry Potter's godfather. According to Sirius, Regulus joined Lord Voldemort's Death Eaters, then panicked at the seriousness of what he was asked to do, tried to back out, and was killed for it. In fact, Regulus turned against Voldemort and stole one of his Horcruxes, hoping to make Voldemort mortal so that he could be defeated, and was killed by the Inferi left as a trap by Voldemort.

Early Life
"...my parents, with their pure-blood mania, convinced that to be a Black made you practically royal...my idiot brother, soft enough to believe them... He was younger than me, and a much better son, as I was constantly reminded..."

- Sirius telling Harry Potter about Regulus

Regulus was born into the House of Black in 1961, the younger of the two sons of Orion and Walburga Black and the youngest member of his entire family. He seems to have been named for his great-uncle, also named Regulus Black, and his paternal grandfather, Arcturus Black. His cousins included Bellatrix Lestrange, Andromeda Tonks, and Narcissa Malfoy, though Regulus likely had no contact with Andromeda after she was disowned and burned off the Black family tapestry for marrying a Muggle-born when he was a child.

According to his older brother, Regulus was exactly the opposite to himself in the eyes of their parents. Although Sirius was the older son and heir, he disagreed totally with the traditional views of his family. His parents disapproved of this and of Sirius's sorting into Gryffindor house at Hogwarts School of Witchcraft and Wizardry, and Sirius eventually left home at the age of sixteen and was subsequently disowned.

Regulus, on the other hand, was regarded as an ideal son for accepting and endorsing his family's values. He was sorted into Slytherin house, and played on their Quidditch team. Harry Potter found a photograph of this team years later; based on the seating, Regulus seems to have been a Seeker.

Joining the Death Eaters
"They’re all about Voldemort. Regulus seems to have been a fan for a few years before he joined the Death Eaters…"

- Hermione Granger on the collage of news clippings in Regulus’ room

From a young age, Regulus admired Lord Voldemort and aspired to become a Death Eater, taking photos and articles about the group from newspapers and hanging them in his bedroom near a painting of the family crest. He was still in his teens when he took the Dark Mark, which the Blacks approved of because Voldemort was seen as striving to achieve pure-blood supremacy over other wizards and Muggles. While Orion and Walburga Black were never Death Eaters themselves, they approved of this ideology.

At some point after becoming a Death Eater, Regulus began to have second thoughts. One of these triggers appears to have been Voldemort's mistreatment of and intention to kill Kreacher, Regulus' loyal house-elf, while setting up the security measures for one of his Horcruxes. It is also possible that Regulus discovered that Voldemort was a half-blood; his cousin Bellatrix Lestrange was shown to be shocked and outraged in 1996 when Harry Potter told her that Voldemort was a half-blood, suggesting that most of his followers were not aware of his true blood status. Regulus may have been dismayed to realize that he had dedicated himself to the cause of a half-blood becoming ruler of the wizarding world.

Defection
"He was murdered by Voldemort. Or on Voldemort's orders, more likely, I doubt Regulus was ever important enough to be killed by Voldemort in person. From what I found out after he died, he got in so far, then panicked about what he was being asked to do and tried to back out. Well, you don't just hand in your resignation to Voldemort. It's a lifetime of service or death."

- Sirius Black

In any case, by 1979, Regulus had defected from the Death Eaters and actively sought to aide the defeat of Voldemort, whom he knew was making use of Horcruxes in an effort to achieve immortality. It appears that Voldemort was aware of Regulus's treachery, since Sirius was aware of it. The Dark Lord probably sought to kill Regulus for it, given the Death Eaters' treatment of other "traitors" such as Igor Karkaroff and the concerns Orion Black, who died the same year as his younger son, had about security.

However, Voldemort was not aware of what Regulus did before his death. He and Kreacher traveled to the cave, where Regulus drank the potion, and Kreacher switched the lockets. Regulus left a note for Voldemort, declaring his desire that the Dark Lord would meet his match when he was mortal. Kreacher, still following Regulus orders, sailed away, watching horrified as Regulus was dragged beneath the lake by Inferi to his death.

Post-Mortem
Kreacher told this story to Harry Potter, Hermione Granger and Ron Weasley in 1997 under Harry's orders, while they sought to destroy all of Voldemort's Horcruxes and realized that Regulus was the mysterious R.A.B. Afterward, Harry gave Kreacher the replica locket that had been left in the potion showing his respect for Kreacher. The house-elf then became much friendlier to Harry, Ron and even Hermione.

During the Battle of Hogwarts, Kreacher rallied the house-elves of the school, calling for them to fight for Regulus where they wielded knives against various Death Eaters's knees and shins.

Physical appearance
Regulus is described as having resembled his older brother, with the black hair and haughty good looks common to the Black family, but Regulus was “smaller, slighter, and rather less handsome” than Sirius.

Etymology
The Black family seems to have a tradition of naming its members after stars and constellations. In Latin regulus means "little king" and was one term for a basilisk. As a name it has also been applied to the star Alpha Leonis, which is situated at the heart of the lion in the constellation of Leo. Regulus was also the family name of a Roman general, Marcus Atilius Regulus, who was known for his honour and self-sacrifice. Arcturus is also a star, in the constellation Boötes. It is derived from Ancient Greek meaning "bear guardian".

Behind the scenes

 * In Harry Potter and the Deathly Hallows, it is established that Regulus was killed by the Inferi in Voldemort's Horcrux cave. But in Harry Potter and the Order of the Phoenix, the way Sirius describes Regulus' death implies that he was killed by the Killing Curse.

Notes and references
Regulus Black Регулус Блэк