J.R.R. Tolkien> The Silmarillion

Elmo was the brother of Elu Thingol (Sindar) and Olwë (Teleri). He lived in Doriath with Thingol and is speculated to be one of the ancestors of Celeborn. He had no parents, at least not in the traditional sense, because he was one of original Elves that awoke at Cuiviénen. By all evidence, he was among the Avari, those who did not make the journey to Aman at the request of the Valar.

                       (Awoke at Cuiviénen)
                                |
                     ___________|___________
                     |          |          |
                  Thingol      Elmo       Olwë
                                |
                             Galadhon
                                |
                         _______|_______
                         |             |
                     Celeborn       Galathil