Elrond was Lord of Rivendell, one of the mighty rulers of old that remained in Middle-earth in its Third Age. His name means “Vault of Stars”, “Star-dome”, or “Elf of the Cave” (the exact meaning is uncertain, as Tolkien gave different derivations in different places).
He was the son of Eärendil and Elwing, and a great-grandson of Lúthien, born in Beleriand in the First Age, making him well over 6,000 years old by the time of the events described in The Lord of the Rings. Elrond’s twin brother was Elros, the first High King of Numenor.
Although Elrond was considered half-elven, that was not meant to be an exact percentage value; he and his brother Elros were also descended from the Maiar, angelic beings who had come to Middle-earth thousands of years before. Elrond, along with his parents, his brother, and his children, were granted a choice between Elven or human fates by the godlike Valar. Elrond chose to travel into the West and live as an immortal Elf, while his twin Elros chose mortality.
In The Hobbit, Elrond gives sanctuary and advice to Gandalf, Bilbo and the Dwarves following their escape from the trolls. He uses his knowledge of runes to name the swords that Thorin and Gandalf obtained from the Troll’s lair, and to identify them, along with the knife that Bilbo later names Sting, as being made in Gondolin by his kin, the High Elves of the West. He also finds the moon letters on Thorin’s map, and provides guidance on the best way to cross the Misty Mountains. Though he does not entirely approve of Dwarves and their love of gold, Elrond chooses to aid their quest because he hates the cruelty and wickedness of Dragons, and because he remembers what Dale was like before it was burned by Smaug.