Our only known dates for Erestor are during the War of the Ring, in which he appeared at the Council of Elrond, and also at the wedding of Aragorn and Arwen the following year. To have become Elrond's chief counsellor, we must presume that he was an Elf of some considerable age and experience. The timeline above presumes that he went with Elrond to Rivendell at the time of its founding in II 1697, but note that there is no direct evidence for this other than Erestor's high standing in Elrond's household.

We have so little detail about Erestor that we cannot even say for sure to which branch of the Elves he belonged. Curiously, he does not seem to have started out as a full Elf at all: Tolkien's earliest notes about the character list him as a 'Half-elf', and even - fleetingly - place him among the members of the Fellowship of the Ring. These ideas seem to have been quickly abandoned, and there is no suggestion that Erestor is anything but a full Elf in later versions of the story.

The name Erestor is not simple to explain, but it can be interpreted (with difficulty, using old and doubtful terms) as 'lonely brother'. If this rather dubious interpretation is correct, it is far from obvious what implication it would carry. Given his brief origins as a 'Half-elf', perhaps Tolkien at one point considered him a member of the family of Elrond Halfelven, perhaps even Elrond's literal brother (though if so, not a trace of this notion remains in the final work). Tor can also refer to a close trusted associate, and it is in this sense - if it appears in Erestor at all - that the term would presumably be intended.

Alternatively, given the overall form of the word, it is conceivable that erestor is an otherwise unrecorded Elvish word for 'counsellor' or 'advisor'. This would fit Erestor's role, but there is no known Elvish stem or root word that would support this interpretation.