"Harry!" Neville burst out. "Harry, Mr. Hagrid's right, you can't, this could all be a trap, they could be after you -"

All of Neville's muscles went rigid and he toppled to the ground, stiff as a board.

A pale-looking Ron Weasley stepped out from behind Neville, his own wand level, and said, "Go."

- Harry Potter and the Methods of Rationality, by Eliezer Yudkowsky

(Not bad for a character that, almost immediately upon introduction, was declared by the main character as not having a reason to exist.)