Who Is R. A. B. ?

I think that Harry needs to search his newly inherited home for the locket, because, I believe Regulus took it and he must have stashed it there somewhere. And, furthermore, Bellatrix is the 3rd brightest star in the constellation Orion.

I checked page 116 in the Order of the Phoenix
It says that they found a heavy locket that no one could open
and that they threw in in the trash bag with everything else.

Is the locket mentioned anywhere else?

Oh wow. I thought that it was obvious Regulus was RAB. Wl in Dutch its RAZ. Z-Zwarts(Black in Dutch). Why else would they translate RAB into RAZ if it wasnt Sirius' brother..

R A B was sirious's brother and an important part of book 6 and 7 in my opinion!

Potterish.com EN [Year 6] - Your Source of News About Harry Potter, JK Rowling, Fanfics, Movie 6 and Book 7
18-year-old actor Tom Moorcroft will play Regulus Black. "Exclusive interview" April 6, 2008. (He never read HBP.)

My problem: I don't remember Reggie doing anything at all until Kreacher tells the story in DH.

Tom Moorcroft Discusses his role as Regulus Black in "Half-Blood Prince" - The Leaky Cauldron
He does confirm he worked only one day, "...it took about 2-3 hours to complete the shot."

That suggests to me that it's just a cameo, introducing the character for later.

I agree, When I remembered the locket that they couldent open in book 5 I asumed it was Regulus, especially when Sirius says that Voldemort killed him. Great minds think alike...