Oh where to begin with someone who may actually be one of the oldest elves in the story....
Might be? Yes might be. Tolkien wrote about 2 Glorfindel characters and in his notes (not considered cannon by some) he linked the two. I will give you the best summary I can for several thousand years of history.
|Glorfindel from LOTRO Lorebook|
As far as his role in Lord of the Rings Glorfindel is the elf that is sent out of Rivendell to find the Aragorn and the Hobbits. The elves of Rivendell know that the Black Riders are in search of them. And Glorfindel takes to the road, arguably the most dangerous task. He is the one who leaves a Beryl on the Last Bridge to signal to Aragorn that the elves are looking for them and scouting the area.
At this time Frodo has already been wounded by the Morgul blade and is slowly turning into a wraith himself. If it wasn't for Glorfindel finding the group and slowing the wound's progress even more then Aragorn was able with the athelas. If it was not for Glorfindel's horse Asfaloth Frodo would never have outridden the Black Riders. Frodo would never have gotten across the ford in time for Elrond to have caused the river to swell and swallow the nine.
Yes sorry to break the news movie goers but Liv Tyler did not speak any breathy elvish and take out the nine. It was Elrond and its one of the crappier changed in the movies that I can think of because they completely cut out Glorfindel.
Glorfindel would be present at the Council of Elrond to decide the course of action about the One Ring.
But why is Glorfindel so important? Early in the 3rd age Glorfindel lead the elven forces from Rivendell to battle Angmar when first the Witch King marched on Fornost. And it was Glorfindel that spoke the words