Harry Potter and the Chamber of Secrets
Like Ginny, Neville is another one of those background characters in the early novels who have the potential to be main characters in the later books. As of Chamber of Secrets, he's still mainly notable for being "a round-faced and accident prone boy with the worst memory of anyone Harry had ever met" (6.1). Neville has almost no confidence in himself. He buys special (clearly fake) charms to protect him from Slytherin's monster because, "They went for Filch first […] And everyone knows I'm almost a Squib" (11.25). Of course, Neville is far from being a Squib: he's got the potential to be a great wizard so long as he can build up his belief in himself. Yet that process hasn't started by Book 2.