Chacho is a Lost Boy who becomes one of Matt's best friends. In fact, you might say he's Matt's first real friend. Matt wasn't exactly Mr. Popular in Opium.
When we first meet Chacho, he seems really sarcastic and angry and mouths off during Raúl the Keeper's speech:
"The orderly production of resources is vital to the general good of the people."
"Crot the good of the people," muttered Chacho, still sanding the wood. (26.49-50)
We think we've got his number; he's a tough guy, with a smart-aleck attitude. This is not a kid who's happy with his situation, and at first, it seems like he and Matt might not end up being friends. But eventually he shows us and Matt more sides to himself. For one thing, he's a very loyal friend, and he quickly decides that Matt is worthy of that loyalty. Thankfully, by the end of the novel, he and Matt have developed a faithful friendship.
As we learn more about Chacho, we begin to understand how such a friendship is possible. He's a sensitive guy. He gets upset if anyone says anything bad about his mother, who died when he was six. And he's steadfast in his belief that his father is alive, even when he's got no proof. He tells Matt, "I'm no orphan! My dad's living in the United States. He's got so much money; he can't even fit it into his pockets; and he's going to send for me as soon as he buys a house." Our narrator tells us that even though he says these words in anger, "Matt could tell from his voice that tears weren't far below the surface" (27.105).
Although he's quite the realist, and constantly questions the ideals of the Keepers, Chacho is nothing but an idealist when it comes to his father. He refuses to believe that his dad is dead or that he has ended up a "zombie" in Dreamland. This mix to Chacho's character comes out again near the end of the book. When Matt jumps on Jorge to protect Fidelito, Chacho joins in wholeheartedly, unafraid of a fight.
But when Chacho and Matt are trapped in the boneyard, Chacho panics. After all, though he's tough on the outside, we're still dealing with a young boy: "Chacho kept screaming, but he must have heard Matt's advice because he didn't struggle. After a moment his cries stopped and were replaced by sobbing" (33.40). Matt, who after all his struggles is probably more mature than his age might ordinarily suggest, is able to keep cool and tries to soothe Chacho. But Chacho, for all his earlier bravado, can't keep his cool.
While he's a tough guy who we'd love to have as a friend, he's not a fully grown macho man. In the boneyard, he's just as vulnerable and afraid as a you might expect Fidelito to be. His freak out also provides a change for our hero to save the day, and Matt proves just how much he cares for Chacho by talking him through the ordeal. We get the ultimate confirmation of their friendship at the end of the novel, when Chacho is one of the three Lost Boys Matt invites to live with him in Opium.