Harry Potter and the Deathly Hallows
Affiliation: Order of the Phoenix
We barely see Bill at all here, but he doesn't let us down – he's a Weasley through and through, spirited and loyal. He's recovered from his werewolf attack in Book 6, and has found his role in the grownup world – as an Order member, as Fleur's husband, and, eventually, as a father (of Victoire). He's also a canny and observant character; he gives Harry some good advice (that goes woefully unheeded) about dealing with goblins.