The Fellowship of the Ring encountered Rúmil and his brothers on 15 January III 3019, and this is the only definite date we have for him. As one of the Silvan Elves, Rúmil might have lived in Lórien for many centuries or even millennia, but all we can we say with certainty is that he was extant at the end of the Third Age.

The name Rúmil goes back to the earliest phases of Tolkien's work, in the person of an ancient loremaster who invented the art of writing. There are several instances of Tolkien taking names from his earlier works and incorporating them into The Lord of the Rings, and Rúmil seems to be one of these. Nonetheless the name does not appear to have been given arbitrarily. The original Rúmil's name seems to have derived from words for 'secret' or 'whisper', and those meanings fit Rúmil of Lórien too, in his role as a stealthy guardian of the Northern Fences. The implication of secrecy and stealth may also connect with the name of his brother Haldir, of whose name one interpretation is 'hidden one'.