I totally forgot, but the initials r.a.b in hp was regulus black right? and he was the one who destroyed-->?

the hocrux when hp and dumbledore went to the cave in half blood prince? I honestly loved the books but i totally forgot how tht story line went, can someone refreshen it for me? And did sirius have another bro? and i thought regulus was a death eater, so if he did destroy the hocruz y wud he?