Is R.A.B evil in Harry Potter and the Half-Blood Prince?

Answer 1

R.A.B. is Regulus Arcturus Black the younger brother of Sirius.

He was a death eater and loaned his house elf, Kreacher, to Voldemort who needed to complete a task. Voldemort was hiding his Horcrux in the cave and needed something worthless to drink the potion for him. The only reason Kreacher survived is because Regulus specifically told Kreacher to return home - and a house elf never disobeys a direct order.

Regulus asked Kreacher what happened and through this information, discovered the Horcrux. Kreacher took Regulus to the cave, although this time Regulus drank the potion. The potion made him weak and he died in the cave after giving the locket to Kreacher and telling him to destroy it.

Regulus is never seen in the books so much of his character is unknown. Indeed, his brother didn't have a high opinion of him, but he was also very biased. Regulus grew up surrounded by a family who hated muggles, it wouldn't have been surprising that he joined the death eaters. But he clearly had a consciousness and died doing something good.

It's important to note that Voldemort took Kreacher along so he wouldn't have to drink the potion, whereas Regulus didn't force his elf to drink it, resulting in his own death. An evil person would have made the house elf drink it.

Answer 2

No, he might have been misled, but he was not evil.