Who is Earendil from The Silmarillion and what is their importance?

Earendil, referred to as Halfelven, the Blessed, the Bright and the Mariner, is the son of Tuor and Idril. He escapes from Gondolin when it falls and weds Elwing, Dior's daughter. He sails with her to Aman and pleads with the Valar for help against Morgoth. The Valar cause his ship, Vingilot, to be able to sail the skies, set with the Silmaril that Beren and Luthien brought out of Angband. He guards Morgoth's imprisonment in the Timeless Void.