Who is the elf in Irish legends?

The modern concept of Elves are in many ways based upon the works of J R R Tolkien, whom in turn based his work upon the ancient legends of the Sidhe, part of the mythological history of Ireland. In fact, by projecting the author's probable intentions as an anti-industrialist, and placing the horrific industrial state of Mordor onto a map of the British Isles as London, and The Shire as The West Country, one can easily see Tolkien's intention to create a mythology for England through his novels that interlinked with existing European Mythology - thus, the Sidhe's ancient arrival in Ireland can be linked with Tolkien's Elves departing middle-earth (mainland Britain) for the Undying Lands.