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Ron is Harry's first and best friend at Hogwarts (not counting Hagrid). They are BFFs from the get-go. Ron spends much of his time being overshadowed by his friends and family. Ron's closest friends are an international celebrity (Harry) and a brainiac (Hermione), and he feels intimidated by all his older brothers' reputations. Whether they're pranksters or high-achievers, they're all making names for themselves in the big bad world, and as the youngest of the Weasley brothers, Ron's worried he won't measure up. That's why, when he looks into the Mirror of Erised, he sees himself winning everything and earning every award, in charge of everybody, and doing everything really well:
"I am [head boy] – I'm wearing the badge like Bill used to – and I'm holding the house cup and the Quidditch cup – I'm Quidditch captain, too!" (12.155)
Ron comes from a long line of wizards on both sides of his family, making him a pureblood. This would normally give his family a higher status in the wizarding world. However, the Weasleys don't have very much money. This doesn't matter much to people like Harry and Hermione, but it does to snobs like Draco Malfoy. It also matters to Ron. He's ashamed of having less, like when he's not able to buy snacks on the Hogwarts Express like Harry is. When Malfoy attacks his family's status, he defends himself and his family courageously. Ron wants to be a Gryffindor because it's the house that his whole family has always been in. Gryffindor is a perfect fit for Ron. He may not cunning, dutiful, or overly wise, but he is brave and smart (Gryffindor traits). He also plays a great game of wizarding chess, and that's no small feat.
Ron is also Harry's – and our – guide to much of the wizarding universe that lurks underneath the Muggle realm. We learn as much about the wizard world from his reactions to Harry's explanations of Muggle behavior as we do from his explanations to Harry about wizard rules and regulations. In a way, the non-magic world is stranger to Ron than the magic world will ever be to Harry or Hermione. He's grown up steeped in magic and speaks the language of magic too well – it's too much inside of him – to ever cross over and attempt to lead an ordinary life.