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.

Source: http://en.wikipedia.org/wiki/Glorfindel