R.A.B. in Harry Potter is Regulus Arcturus Black.
He stands out as a pivotal yet understated figure whose bold move against Voldemort reshaped the series' fate.

Core Identity

Regulus Arcturus Black, often just called "R.A.B.," was Sirius Black's younger brother from the infamous pure-blood Black family. Born in 1961, he attended Hogwarts, got sorted into Slytherin in 1972, and idolized Voldemort early on, joining the Death Eaters as a teen. Unlike his rebellious brother Sirius (a Gryffindor), Regulus embodied the family's dark traditions—until he didn't.

His initials first pop up mysteriously in Harry Potter and the Half-Blood Prince , scrawled inside a fake Horcrux locket:

"To the Dark Lord,
I know I will be dead long before you read this but I want you to know that it was I who discovered your secret. I have stolen the real Horcrux and intend to destroy it as soon as I can.
I face death in the hope that when you meet your match, you will be mortal once more.
R.A.B."

This note, found by Harry, Dumbledore, and later the trio, sparks fan theories galore back in 2005—long before the big reveal in Deathly Hallows.

His Daring Horcrux Heist

Regulus uncovered Voldemort's immortality secret (splitting his soul into Horcruxes) after sending his loyal house-elf Kreacher to the deadly cave as a test run. Kreacher drank the potion, survived the Inferi, and confirmed the locket's dark power. Fueled by regret, Regulus returned with Kreacher, swapped the real Salazar Slytherin locket for a decoy, and drank the potion himself.

  • They escaped, but Voldemort's forces killed Regulus soon after—he was just 18.
  • The real locket ended up back at Grimmauld Place, hidden among junk, until Harry, Ron, and Hermione retrieved it. Ron destroyed it with the Sword of Gryffindor in Deathly Hallows.

This selfless flip humanizes Slytherins, showing not all pure-bloods were irredeemable. Picture a starry-eyed kid turning into a quiet hero, dying alone but weakening the Dark Lord for good.

Family Ties and Rivalries

Regulus shared the Black family tapestry (at Grimmauld Place) with Sirius, but their paths split hard—Sirius fled the family, while Regulus dove into darkness before his turnaround. Fans love debating this brotherly contrast: Sirius's loud defiance vs. Regulus's secret sacrifice.

Brother| House| Voldemort Stance| Fate
---|---|---|---
Sirius Black| Gryffindor| Rebelled openly| Killed at Dept. of Mysteries 3
Regulus Black| Slytherin| Joined, then betrayed| Drowned by Inferi in cave 59

Fan Buzz and Legacy

Even in 2026 forums, R.A.B. stirs debate—some call him a "tease" for stealing Snape's redemption arc spotlight, others hail him as peak complexity (a flawed Death Eater finding light). Reddit threads from 2022-2025 question if he'd still exist in a tighter plot.

No major latest news shakes this up; his story's locked in Rowling's canon, fueling fanfic and House of the Dragon-style "what if" chats.

TL;DR: Regulus Black (R.A.B.) was Sirius's Slytherin brother who stole and tried destroying Voldemort's locket Horcrux, dying young but aiding Harry's win.

Information gathered from public forums or data available on the internet and portrayed here.