Elemmakil was an Elf of Gondolin.
Elemmakil was the captain of the guard protecting the Outer Gate. He was the first to encounter both Tuor and Voronwë when they had found their way through the cavern that led to the first of the gates. After a brief discussion about who they were and what they were doing there, he accepted them and led them through the Seven Great Gates until they reached Ecthelion, the Warden of the Great Gate.
He apparently knew Voronwë when he lived in Gondolin.