Eärendil is the fictional star that guides the Elves in J.R.R. Tolkien’s mythology.
Eärendil is a Half-elven mariner who sails to the Undying Lands seeking help for the peoples of Middle-earth during the First Age. His voyage leads the Valar to intervene against Morgoth in the War of Wrath.
After Eärendil reaches Valinor, he is placed in the sky with the Silmaril on his brow. The light of the star becomes a sign of hope for Elves and Men. In The Lord of the Rings, Galadriel gives Frodo a phial containing light drawn from that star.
Varda, also called Elbereth, creates or places the stars but is not herself the star. Anar is the Sun, and Tilion is the Maia who guides the Moon. These are related celestial figures, not the requested star.