The younger brother of Sirius Black, Regulus Arcturus Black (R.A.B) was a Slytherin like most other members of his family. He had initially been a member of Voldemort’s Death Eaters before eventually turning against his master. When he left Voldemort’s ranks, he managed to steal one of Voldemort’s Horcruxes, the Slytherin locket, with the intention of destroying it.