Thanks to everyone who took a stab at my trivia question! I know that for some of you pros, it was probably no sweat.
Teresa was the first to answer correctly — congratulations, Teresa!
The answer is Charlie. Ron had been given his older brother Charlie’s wand when we first met him in The Sorcerer’s Stone. Ron’s first wand (or, Charlie’s old wand) was broken during his encounter with the Whomping Willow in the beginning of Chamber of Secrets. His wand never worked the same after that. When Lockhart used Ron’s wand to obliviate Ron and Harry, the spell backfired, which left Lockhart in a permanent state of amnesia. Ron eventually purchased a second wand with Mr. Weasley’s winnings from the Daily Prophet contest.
— Amanda, Harry Potter Message Board Moderator