R.A.B. was Regulus Arcturus Black.
He was the younger brother of Sirius Black. In the books, his initials are found on a note left inside a fake locket. That note says he found Voldemort’s secret, stole the real Horcrux, and meant to destroy it.
This is not an unsolved mystery in the finished book series. Harry Potter and the Deathly Hallows explains who R.A.B. was, through Kreacher’s account.
Regulus Black at a Glance
- Full name: Regulus Arcturus Black
- Family: Younger brother of Sirius Black; son of Orion and Walburga Black
- Hogwarts house: Slytherin
- First loyalty: The Death Eaters, under Lord Voldemort
- Later action: Turned against Voldemort and tried to destroy a Horcrux
- Death: 1979, in the seaside cave where the locket was hidden
Regulus was born in 1961. Exact month and day are not given consistently in secondary sources, so this article uses the year only.
Who Was Regulus Black?
Regulus grew up in the pure-blood Black family at 12 Grimmauld Place. Unlike Sirius, who was sorted into Gryffindor and rejected much of the family’s outlook, Regulus was sorted into Slytherin.
He joined the Death Eaters while still young. At that stage, he supported Voldemort and the pure-blood ideas his family valued.
The books do not present him as a member of the Order of the Phoenix. He did not help the Order with information about Voldemort’s movements. That claim in older summaries is not canon.
How the R.A.B. Mystery Is Solved
The mystery starts in Harry Potter and the Half-Blood Prince. A mysterious person signs a note “R.A.B.” inside a locket.
Later, in Harry Potter and the Deathly Hallows, Harry and Dumbledore travel to a seaside cave. They find a locket, but it is a fake. Inside it is the note from R.A.B.
Harry later sees the name on a bedroom door at 12 Grimmauld Place: Regulus Arcturus Black. The initials match.
The full story then comes from Kreacher, the Black family’s house-elf. Kreacher was there. His account, told in Deathly Hallows, fills in what Harry could not have known on his own.
What Is a Horcrux?
A Horcrux is an object that holds part of a wizard’s soul. Voldemort made Horcruxes to try to avoid death.
One of them was Salazar Slytherin’s locket. Voldemort hid it in a seaside cave, guarded by a potion and by Inferi in a lake. Inferi are reanimated dead bodies under dark magic.
The locket was not one of the Deathly Hallows. The Deathly Hallows are three separate objects: the Elder Wand, the Resurrection Stone, and the Cloak of Invisibility. Regulus did not retrieve the Resurrection Stone for Harry.
Kreacher and the Cave
Kreacher’s story explains why Regulus changed sides.
Step 1: Voldemort borrows Kreacher
Voldemort asked Regulus for the use of his house-elf. He took Kreacher to the cave to test the defences around the locket Horcrux.
Kreacher was made to drink the potion guarding the locket. Voldemort then left him there to die. Kreacher escaped using house-elf magic that Voldemort had not accounted for, and told Regulus what had happened.
Step 2: Regulus returns with a fake locket
Regulus decided to act. He took Kreacher back to the cave, carrying a substitute locket with the note for Voldemort inside it.
Kreacher guided him past the cave’s defences to the island and the basin holding the locket.
Step 3: Regulus drinks the potion
Regulus ordered Kreacher to take the real locket once the potion was gone, replace it with the fake, leave without him, and try to destroy the real one.
Regulus then drank the potion himself. When he tried to drink from the lake, he was dragged under by the Inferi and died.
He was not killed by Death Eaters in a battle. He died in the cave, during this attempt to remove and destroy the Horcrux.
Why Did Regulus Turn Against Voldemort?
The books give a clear trigger: what Voldemort did to Kreacher.
Regulus saw, through Kreacher, how Voldemort treated a loyal servant as disposable. He also learned that Voldemort had split his soul to pursue immortality.
That was the point at which Regulus acted against his former master. The books do not give a full inner monologue for Regulus. His exact private thoughts are not spelled out.
So it is fair to say this: his actions show a break with Voldemort, driven by the Kreacher episode and the Horcrux secret. It is not fair to claim he had rejected every pure-blood belief, or that he had joined the Order. The books do not prove that wider change.
What Happened to the Locket After Regulus Died?
Kreacher obeyed Regulus, but he could not destroy the real locket. He kept it at Grimmauld Place.
Later, Mundungus Fletcher took it from the house. It then passed to Dolores Umbridge. Harry, Ron, and Hermione later tracked it down.
Ron Weasley eventually destroyed Slytherin’s locket with the Sword of Gryffindor. That completed, years later, what Regulus had set out to do.
Harry also gave Kreacher the fake locket. It was a mark of respect for the elf, and for Regulus.
What About the Films?
The main facts above come from the books, mainly Deathly Hallows. The films cover far less of Kreacher’s tale than the book does.
If a film-only viewer is confused about R.A.B., that is understandable. The book version is the fuller account, and it is the version used here.
Common Questions About Regulus Black
Was Regulus a hero?
He started as a Death Eater. He ended by giving his life to weaken Voldemort. That change is what makes him interesting. It does not erase his earlier choices.
Did Regulus betray Harry to Voldemort?
No. He acted against Voldemort, in secret, and died before Harry’s story began. He never met Harry.
Was Regulus killed in 1979 by Death Eaters?
No. He died in 1979 in the cave, dragged under by the Inferi after drinking the potion.
Did Regulus play Quidditch?
A photograph found later suggests he played as Seeker for the Slytherin team, based on the seating in the team photo. That detail is suggested, not firmly stated, in the books.
Why Regulus Matters to the Story
Regulus matters because he proves an early point in the series: Voldemort’s secret was not safe forever.
Long before Harry began hunting Horcruxes, someone inside Voldemort’s own circle had found one, stolen it, and died trying to destroy it. Harry’s hunt builds on that first, failed attempt.
