Who is Luna Lovegood from Harry Potter and the Deathly Hallows and what is their importance?

Luna Lovegood is friends with Harry, Ron, Hermione, and Neville. She is willing to support Harry no matter what the cost. When Luna is taken away to the Malfoy Manor as a prisoner, she remains true to her convictions. She is a bit eccentric, but she is always very open to the unlikely.