(big red ticklish thing? lol)
Elmo is only mentioned in the Unfinished Tales in discussions on Galadriel and Celeborn. Because Celeborn is in the Silmarillion presented as a "kinsman of Thingol", Tolkien wished to develop this family link. One of his solutions was to establish Celeborn as the grandson of Elmo, a non-important brother of Elwë who remained behind when Elwë was lost, becoming one of the Sindar of Doriath. In this conception Elmo has a son named Galadhon, who in turn sired Celeborn and another son named Galathil, who was the father of Queen Nimloth of Doriath.