Legolas: Legolas is an archer and part of the Fellowship of the Ring. He is brave and passionate. While Elves and Dwarves are the biggest enemies in this world, Legolas gets along quite well with Gimli. They are always making everything a competition between themselves on their adventure. When he gets separated from Frodo, he travels with Aragorn and Gimli for the rest of the trip.
Elrond: Elrond is the king of the elves in Rivendell. He is the father of Arwen, the love interest of Aragorn, and is very protective of her. He is consulted by many for advice. He reads the inscriptions on the One Ring. He also reforges the shards of Narsil in Anduril for Aragorn.
Arwen: Arwen is the the love interest of Aragorn, and she loves him back. She gave him her light in a necklace. It is what kept her alive forever as an elf. But now, neither of them will live forever. She was willing to die to be with him instead of living without him for many ages. When she gets sick from doing this, Aragorn feels it and only becomes more encouraged to stop Sauron and to help her.
I did not know all of this, so please check out my references.