What is "glorfindel"

In the fiction of J. R. R. Tolkien, Glorfindel is a name used twice for an Elf appearing in the tales of Middle-earth. He is introduced in various material relating to the First Age of Middle-earth, including The Silmarillion. The second instance is for a character of The Lord of the Rings, which takes place in Middle-earth's Third Age. In later writings, Tolkien states they were one and the same, though this is not evident from The Silmarillion and The Lord of the Rings.

The character and his name (meaning "blond, golden-haired") were among the first created, when Tolkien first conceived of what would become his Middle-earth legendarium in 1916–17.