I have a theory who R.A.B. is. He’s mentioned at the end of Harry Potter and the Half-Blood Prince… oh yeah, spoiler alert. Anyway, it’s Regulus Black. He’s the younger brother of Sirius who joined the Death Eaters, left the Death Eaters and was offed in some as-yet-unmentioned manner by Voldermort or “on Voldemort’s orders, more likely” (pg 112 in OOTP).
1) The initials. We don’t know his middle name, yet, but two out of three is pretty good.
2) He was murdered by Voldemort just after trying to leave the Death eaters which implies he was high up in the evil-doers’ chain of command. If he was close to Voldemort, he could have known about the Horcruxes and that would have made it easier for him to find the locket.
3) Sirius, and all the rest of the Black family, actually, is dead so they can’t give any info on Regulus. Sidenote to JK Rowling, who I’m sure is an avid reader of my blog: No more Pensieve scenes unless they involve Harry’s parents meeting and falling in love, ok? They’re starting to feel like page-count increasers and plot cop-outs.
4) There is a “heavy locket that none of them could open” (pg 116 in OOTP and I promise I’ll stop footnoting now) in a dresser at 12 Grimmauld Place. Coincidence?
5) Unfortunately, Mundungus Fletcher swiped a bunch of the Black family silver and pawned it in THBP, so the locket could be anywhere. Hence, the seventh book.
6) Rowling is really into the classicist-friendly foreshadowing. Some of it’s a bit much, like Sirius becoming a dog and Remus Lupin becoming a wolf.
And Regulus is the name of a Roman general who was taken prisoner by the Carthaginians in the 2nd Punic War. He was given an opportunity to return to Rome to a peace treaty, which he did, then he told the Roman senate not to accept them (even though those terms made provision for his life + return to Rome) because the terms sucked for the OotP, I mean, for Rome as a whole. He went back to Carthage with the answer, instead of running away which he totally could have gotten away with,, and then Voldemort, I mean, the Carthaginians, killed him.
Your tuition dollars at work, Mom and Dad.