Many Harry Potter readers are theorizing about the identity of R.A.B. The initials at the bottom of the piece of paper folded into the false locket, taken from the Cave Basin, inspire a roster of possibilities. Was it Regulus Black? Borgin, or Burke, of the Dark Arts shop where Tom Riddle was once employed? Another member of the Black family? Is it someone's nickname? Following are some guesses about R.A.B., and circumstances surrounding R.A.B., in HBP (Half-Blood Prince.)

What if the R.A.B. on the note in the false Horcrux locket did not refer to whom, but to what? What if R.A.B. was an abbreviation of a phrase, or spell, or special knowledge shared only by LV (Lord Voldemort) and the writer of the enclosed note? If this is indeed the case, it would let LV know that it could've been written by only one person. It could not, then, be a forgery or misrepresentation by anyone else. Who might so boldly taunt the DL (Dark Lord) with this revealed deception of stealing the true Horcrux locket, stating it would be destroyed by the writer, and conclude with a wish that the DL would fail in his quest for Immortality? A good candidate for this would be Severus Snape.

Snape was, like Tom Riddle, a Half-Blood, clever, from apparently sad family circumstances, from a situation in which he felt rejected, and possessing a natural affinity with the Dark Arts. As Slughorn said of the Dark Arts, "Wizards of a certain caliber have always been drawn to that aspect of magic..." (p. 498, HBP), and both Riddle and Severus were gifted. Unlike charming, charismatic, popular Riddle, Snape was unpopular, a target for bullying and ridicule. Riddle, perhaps with the guidance of unwitting, connections-fostering Slughorn, would've found Severus Snape easy to recruit to his cause. As a DE (Death Eater), Snape may've felt that he finally belonged somewhere. He may've felt powerful, his considerable talents valued, his standing as a DE superior to those who ridiculed him. Snape's initials were even the same as the revered Pureblood Salazar Slytherin, with whom he might identify as a member of Riddle's power-seeking clan. Under Slughorn's tutelage, Riddle may've seen the mechanics of how to cultivate and collect those students, such as Snape, who would eventually support his cause. Riddle could have "...great power and influence over young witches and wizards." (p. 431, HBP.) Riddle could attract them with charm and brilliance, and later, hold them with fear as LV.

After his school days had ended, as the ranks of the DEs grew, perhaps Severus became a sort of First Lieutenant for LV. Snape, with his virtuosity in Dark Arts and Potions, and his superb Occlumens/Legilimens talents, must've proven a valuable asset to LV and his operations. Severus, with his uncanny knack for turning up where the action was, was there when the Prophecy was uttered by Professor Trelawney (p. 549, HBP.) He told LV what he knew of the Prophecy (the first half), probably thinking the Pureblood family of the Longbottoms were meant as LV's equal. He would not have guessed that LV would choose the Half-Blood, Harry Potter, as his most potentially dangerous rival.

Back in Snape's school days, when James used Snape's own Levicorpus spell against him (in Order of the Phoenix, Snape's Worst Memory), Snape seemed to be internalizing LV's brand of pureblood mania. He calls Lily Evans, his talented, popular defender, a Mudblood. She seems surprised at his slur. Because of Lily's dazzling skill at Potions, and her acceptance of others whatever their popularity (or lack), perhaps Snape had a grudging regard and respect for his classmate...initially. Under LV's patronage, Snape apparently distanced himself from Lily, and anyone else in her Blood Category.

With LV's choice of Harry, the Half-Blood, to kill as a result of the Prophecy, Snape may've realized he was in danger. If LV saw Harry as his equal, and would not tolerate him as a potential rival, how much more might he keep an eye on gifted, knowledgeable, clever Snape? Would LV dispense with Snape as he did so many others? Would Severus, thinking he was valued, and superior to those who did not know how to seek power and use it, become one of LV's Inferi one day? After LV had extracted everything from Snape he felt he needed to, Severus might be eliminated.

Snape may also have made a regrettable error if he informed LV of Lily's gifts and skills as a witch (although Slughorn may've been responsible for this, also). Perhaps Snape thought his master would be pleased to know of Lily's capabilities, and would credit Snape with bringing her considerable talents to serve in his cause.

LV turned up at Godric's Hollow. He perhaps offered Lily a place with the DEs on Snape's description of her, and presented it as a chance for Lily to save herself. Of course, Lily must've refused--"Stand aside, you silly girl" LV says, and later says she needn't have died. LV must've thought her an utter fool not to save her own skin, in the face of the inevitable. James was already dead, and Harry was about to die. Perhaps if Lily had lived, she would've been Imperiused or otherwise forced into LV's service, because Snape had described her capabilities to LV.

Snape probably witnessed the murders at Godric's Hollow. After seeing what had happened with the failed AK curse, Snape, with his knowledge of Dark Arts and LV, knew the DL would not stop until he had found a way to inhabit a body again. The callous disregard in which LV had dismissed the Potters' lives and potential usefulness to him, may have made Severus realize his own position. Snape's Dark Arts virtuosity, commitment, and role of close personal advisor and spy, meant nothing to LV the sociopath. Snape could be just as summarily dispatched with as the Potters, at LV's whim. Snape may also have realized the DL's tactical weaknesses, created through his arrogance and perverted use of Horcruxes. Should LV be able to regain a body, he could fail in his final attempts through his errors, and then Snape would fall into the hands of Albus Dumbledore and the Order. Snape had to bide his time and act judiciously until he saw what would happen with LV regaining power. Snape would act to save his own skin, in Slytherin-like tradition.

Snape’s only hope? Dumbledore. Dumbledore, after hearing him out, realized that Severus would aid and abet the Order of the Phoenix only because it would aid his own survival, not because it was the right thing to do. Even if LV came back into power and defeated Dumbledore and the Order, Snape still might not survive if he was on the DE side. LV would countenance no rivals, and Snape might know too much for the DL to tolerate him past a certain point. Despite how distasteful it must've been to aid and support Harry and certain members of the Order with whom Snape had an unpleasant history, he knew what he had to do to stay out of Azkaban. Snape joined the Order.

Severus had come to the right conclusion, in spite of himself.

While waiting to see when LV might regain a body, Snape began to develop his double-agent role. He could then take advantage of whichever side might benefit him at certain times, in the future. Feeling as he did toward Harry, it didn't take much acting skill to present a cruel, bullying demeanor to Harry, his friends, and their sympathizers. Teaching in front of a classroom which included the children of DEs must've meant they would tell their DE parents about Snape's favoring of them and all Purebloods. At this time, Snape could be gathering more information and magical knowledge at Hogwarts, since the School had more "...mysteries to unravel, stores of magic to tap." (p.431, HBP.) Concurrently, he had to collaborate with Dumbledore on LV, the Dark Arts, and plot strategy for the time when the DL reappeared. Dumbledore must have felt that this was not a question of if, but when. Snape needed to aid the Order so that Harry's chances of succeeding were bolstered. If the Order triumphed in the end, Snape's chances of surviving were better, too. Snape continued to bide his time, gather information for his own purposes, and keep himself out of Azkaban.

How far would Snape commit to the Order? During the Unbreakable Vow he performed with Narcissa at Spinner's End, Snape's hand twitched (p.36, HBP). By taking the Vow, Severus is ramping up the danger factor for himself. He is treading an ever thinner line. He thought he would have to do this to keep his cover with LV and the DEs, but it means he will have to manipulate Draco himself by seeming to help, so he is in accordance with the Vow (p.323, HBP). Or, he would have to convince Draco that Dumbledore was right, he could hide Draco and his mother "...more completely than you can possibly imagine."(p. 592, HBP.) In other words, appear to be dead.

In the Spinner's End chapter of HBP, Draco's task from the DL is not clearly defined as murdering Dumbledore. "The Dark Lord's wishes", "The deed the Dark Lord has ordered Draco to perform", and the like, are used. Draco has obviously interpreted LV's orders as "kill Dumbledore", either verbatim, or as a means to achieve the DL's task. Draco has also communicated this to the DEs who invade Hogwarts through the two cabinets. LV wouldn't care if Draco misinterpreted his order, since its purpose was to punish Lucius’ bungling, with a task which would lead to Draco's death. What was the task? Snape would have to see it fulfilled on Draco's behalf, or die. Perhaps it was that Dumbledore must be expelled from Hogwarts forever. Hogwarts, the Order, and the Ministry of Magic would collapse without Dumbledore there. Draco may've assumed murder was the only avenue which he himself could manage to ensure that Dumbledore could not return to Hogwarts; Snape could possibly finesse a result which would fulfill Draco's task/the Vow that did not involve murder. Dumbledore might be spared, and continue to direct operations from a location outside Hogwarts. The Order, the Wizarding World, and the Ministry of Magic would be spared as well. Draco and Snape could then "hide in death", courtesy of Dumbledore.

It would seem that Dumbledore had other plans for Severus Snape, than to allow him to relinquish his difficult and distasteful Order and DE duties and go into hiding. Dumbledore seemed to want Severus to step up to the plate, to be given the whole responsibility for making Harry his protégé, to single handedly do everything possible to see that Harry's task as The Chosen One succeeded.

Dumbledore wore the Gaunt ring after LV's soul fragment in it was destroyed. It served as an advertising beacon to LV and the DEs that the Order, or at least Dumbledore, knew about the Horcruxes. LV is now likely to take stock of his remaining Horcruxes, thus creating a chance for Order spies (especially Snape?) to discover their whereabouts. Who may've originally guessed where the Locket, the symbol of Salazar Slytherin passed down to his heirs, had been hidden? Severus Snape. Severus, with his Dark Arts and Potions skill, and his inside track knowledge of LV, has discovered it. He is able to extract the real locket, and put the false one with the note in its place. If anyone could deal with that green potion in the basin in the cave, draining then replacing it, it's Snape.

Why would he do this? He wants to force Dumbledore to "hide him in death", knowing he'd be pursued and killed (or worse) if LV ever read the enclosed note. Snape may think that his double-agent role is getting too risky, and of course wants to save himself, first and foremost. He also wanted to show that he, Severus, was cleverer than even LV. He stole the Locket, left a taunt for the DL in way of the enclosed note, and left him to wonder if the Horcrux was actually destroyed or not (since LV couldn't feel it if it was.) Snape could show his allegiance to the Order, thus making fools of LV and the DEs. And what did Snape do with the real Locket? Hid it in Grimmauld Place, in plain sight. As he pointed out when Bella challenged him, he cannot speak the name of Order H.Q., since he is not the Secret Keeper (p.30, HBP). The locket would be safe, with the Order members constantly around, and Snape could continue to check on it.

To help force the issue of his hiding, Snape would not tell Dumbledore how to get the false locket out of the basin, but perhaps did hint at the Cave location. Dumbledore guessed about the Horcrux, and went to retrieve it without Snape's help. He had to force Snape to maintain his double-agent role; it was too valuable to give it up yet. With the false locket and the R.A.B. note removed, LV would not know Snape was the one who removed the Horcrux. Dumbledore would not be forced to hide Snape in death.

When Dumbledore came back from the cave, he needed to see Snape. He could not save himself, despite his prodigious knowledge, and Madam Pomfrey couldn't come close. Snape, with his specialized knowledge and skills, was the one able to continue to move forward for the Order, and to guide Harry. On the Tower, through Legilimancy, Snape sees what Dumbledore has done with the false locket, and receives the heavy task of continuing to put himself in harm's way for “The Chosen One”, whom he hates. He and Draco now cannot hide in death. Dumbledore has saved them both, but in doing so, has condemned them both to take flight, with an uncertain outcome with the DL awaiting them. Snape's efforts to disengage himself from his multiplying risks, on behalf of the Order, may've explained the heated argument that Hagrid heard between Dumbledore and Snape (p.405, HBP.) Snape's fury at Harry calling him a coward may've stemmed from Snape wanting to give up and hide in death (p.604.)

As Snape dragged Draco out of Hogwarts, he gained enough of a head start on Harry to stop, look in Dumbledore's robe pocket, and verify that the false locket was there. He left it for Harry to find, per Dumbledore's instruction through Legilimancy up on the Tower. If it fell into DE hands, Snape could explain it away by saying he had to appear to be on the Order's side, so he wrote the note, and defined the R.A.B. signature to Dumbledore to maintain his credibility with him. Severus could claim that he used the R.A.B. purposefully, so the DL would recognize Snape's handiwork, and know that things were actually under control if LV retrieved the false locket out of the basin. Snape could re-establish his trust with LV by simply going back to Grimmauld Place, and retrieving the Horcrux Locket for him if need be. Snape, by leaving the false locket with the note for Harry to find, has established R.A.B. as an ally in the cause to defeat LV. Harry would never trust Snape to guide him, so his final instructions to Harry to keep his mouth shut, and his mind closed (p.603, HBP) may be lost on him. Snape's final act of saving Harry from the Crucio curse may not register with him, either (ibid). However, if Harry responds to information from the anonymous R.A.B. (actually Snape), Severus may be able to assist Harry in the future, from wherever his location will need to be. Just as Harry learned more than he ever had before about Potions from the Half-Blood Prince's book, Harry might find out much valuable information for his quest from Snape as R.A.B.

After Dumbledore was taken out of the picture, Snape was left to continue to tiptoe between the two sides, in an ever more dangerous, razor-thin line. He was trapped in a bitter service to Harry, Draco, the Order, LV, the DEs, and an absent Dumbledore hiding in death. He must've despised all of them at this point. No wonder Snape's face reflected hatred and revulsion, as Dumbledore gently pleaded with him, while they were up on the Tower. Dumbledore was reminding Snape that this was now his only way out. Snape was left with many regrets, including being duped by LV and the Pureblood philosophy, and the actions which led to the death of Lily Potter. She may have been his only friend at Hogwarts.

In HBP, Severus knew that it was his final year at Hogwarts. His coveted post as DADA teacher was cursed, and he knew it. Perhaps Snape took his old Potions book and left it in the cupboard of his old Potions classroom to become a part of the "...small stock of old books..." (p.184) available to students. He may've thought the book could be the only part of him which would survive after he left Hogwarts. Harry stumbled across Snape's legacy when he was lent the Potions textbook for class. It may've been part Lily's legacy, too, if she was playing a game of one-upmanship with Severus, inventing new spells and potions; their friendly rivalry as classmates, in long-ago classes taught by Horace Slughorn, may've been recorded in Snape's cramped handwriting, in the margins of the battered old book.

So, what might R.A.B. stand for? Whatever it is must be inconsequential, compared to the notion that only Snape would know and LV could readily guess what it referred to. This reference would probably have to include the context of finding it in the basin in the cave. It would also have to reflect information in the language which Snape had provided to the DL at one time or another. Just as an example: Three Latin words (probably ersatz!) which could fit the bill:

Res--a point, a particular thing, the matter referred to
Absobeo--to swallow, gulp down, carry away, engross
Bis--twice, a word to show that something is repeated

Snape knows he must eventually extricate himself from LV. The DL might very well see Snape as too dangerous in the future, because Severus has discovered far too much about him, despite his solitary nature. LV might murder Snape/turn him into an Inferius, to maintain his secrets as much as possible. Harry must succeed, and Snape must help in any way he can. Harry's survival, and thus Snape's, depends on it.

In the end, though, what course could Snape's resentful hatred of Harry take? Snape has had to give up a great deal, for the sake of someone he loathes. After fulfilling the necessity of his task to make sure Harry vanquishes the DL, will Snape exact revenge? As the quest is completed, will someone or something Harry loves be destroyed, out of Snape's spite? What will happen as Snape faces Harry, and sees Harry's resemblance to both his parents? Snape has had to choose to go against the Dark Lord, and all that he stands for. In looking at Harry, Lily's eyes remind him why, but James's face and form continue to mock him.