His name literally meant 'Golden-haired'. Throughout the Third Age he helped to protect Rivendell, and in TA 1975 he led a force out to face the host of the Witch-king of Angmar. With the help of Círdan, the enemy's host was destroyed. The Witch-king himself turned and fled at the sight of Glorfindel. At that time, Glorfindel prophecised that the Witch-king would not be killed by the hand of a man.

Glorfindel was one of the most powerful elves alive at the time of the War of the Ring, and one of the few elves powerful enough to ride openly against the Ringwraiths, because he had seen the light of the Two Trees. For that reason, he was sent in search of Aragorn and the hobbits when they were late in arriving at Imladris. He found them, and gave Frodo his horse, Asfaloth, to ride to Rivendell. He then stayed with Aragorn and the other hobbits to fight off the Ringwraiths.

He was one of Elrond's most trusted advisors, and was there at the Council of Elrond, when the fate of the One Ring was decided. He gave the council the only two choices of what to do with it: send it over the sea, or destroy it.

*Note*: It appears, according to some of Tolkien's later writings, that Glorfindel of Gondolin is the same Elf as Glorfindel of Rivendell, who appears in The Lord of the Rings.

Apparently, Elves could be reincarnated after spending time in the Halls of Mandos if they died. After some time spent there, they would be returned to their bodies and could then live amongst their kin in Aman.

If all of this is true, the return of Glorfindel of Gondolin to Middle-earth was a unique occurrence and as far as we know, the same did not happen at any other time.