The exact passage you’re thinking of is as follows (GoF, chapter 33):
“And here we have six missing Death Eaters… three dead in my service. One, too cowardly to return… he will pay. One, who I believe has left me forever... he will be killed, of course… and one, who remains my most faithful servant, and who has already reentered my service.”
As with the answer to a similar question, I’d assume that these people are part of Voldemort’s “inner circle”, and not representative of his entire force. Voldemort doesn’t strike me as the sort of person who’d mourn or mention their loss. I think the losses were far greater than three, but most wouldn’t merit any mention at Voldemort’s rebirthing ceremony.
So, who are these three people? I checked lists of named Death Eaters on HP Wikia, Lexicon, and so on for plausible candidates, and there are only really these three.
Here are my guesses:
We get his name in Karkaroff’s trial (GoF, chapter 30):
“Why, yes... there was Rosier,” said Karkaroff hurriedly. “Evan Rosier.”
“Rosier is dead,” said Crouch. “He was caught shortly after you were too. He preferred to fight rather than come quietly and was killed in the struggle.”
“Took a bit of me with him, though,” whispered Moody to Harry’s right. Harry looked around at him once more, and saw him indicating the large chunk out of his nose to Dumbledore.
Why do I think he’s important?
- Karkaroff thought his name would be of value to the Ministry.
- He was dispatched by Moody, probably the “best Auror the Ministry ever had” (Sirius). This suggests that he was a high-profile (and highly skilled) target.
- Chose to die rather than being arrested, which suggests dedication to his cause and the possibility that he had secret information he wanted to keep out of the Order/Ministry’s hands. Both suggestive of high rank. We also know that Moody “always brought people in alive where possible”, so he wasn’t killed idly.
He died before the end of the war, so Voldemort would have known of his death. Quoting Sirius again (GoF, chapter 27):
“Rosier and Wilkes – they were both killed by Aurors the year before Voldemort fell.”
This is when Sirius is discussing Snape’s old gang, and their future careers as Death Eaters.
All we have to go on is the line from Sirius above. We know he was a Slytherin, student at Hogwarts, in a group with other prominent Death Eaters (inc. Avery, the Lestranges and Snape). Lacking better guesses, this seems like a good guess for the second.
This is more of a wildcard, but hear me out. Here are some arguments in favour:
- He was a pure-blood wizard from a respected family, with close relations to many other pure-blood Death Eaters and their families. This is prime Death Eater material, and likely to ingratiate him with the inner circle. (It may also be why he got cold feet, if he was quickly placed alongside the more ruthless Death Eaters and saw Voldemort in person.)
- He was close enough to Voldemort to find out about the horcruxes. At least in part because he volunteered Kreacher to help place the locket in the basin, which suggests he was trusted by Voldemort. He also knew how to get Kreacher out from the cave, and used Kreacher’s knowledge to retrieve the original horcrux. This suggests cunning and intelligence, which would have been valuable skills as a Death Eater.
- The note he leaves is signed “R.A.B.”, rather than his full name. If he expected Voldemort to recognise this, he was probably of some importance.
- Finally, we know he died in the cave replacing the horcruxes, and kept the circumstances of his death a secret to keep the family safe. Since Voldemort never returned to inspect the locket, he would never have learnt of Regulus’s defection. In this case, it seems logical to assume he died loyal to Voldemort and during his service.