Harry Potter and the Half-Blood Prince Luna Lovegood (Evanna Lynch)

Luna has definitely become part of Harry, Hermione, and Ron's extended circle of loyal buddies. Sure, she's a little…eccentric, but she's super reliable in a pinch.

Case in point: if she hadn't been wandering around the Hogwarts Express wearing strange glasses and looking for who-knows-what, Harry would have remained invisible and incapacitated on the floor of the train (courtesy of a run-in with Malfoy) for a long time:

LUNA: Hello, Harry!

HARRY: Luna. How'd you know where I was?

LUNA: Wrackspurts. Your head's full of them.

Um...sure? Because that sounds like something that could happen.

We also love that she shows up to Gryffindor Quidditch matches wearing a roaring lion hat to show her support (when Ravenclaw isn't playing, that is). Again, it's eccentric, but also totally awesome.