Fahrenheit 451 doesn't have what I would call true chapters. The book is divided into three long parts. I'll give a brief overview of the first two main characters introduced in part 1.
The first character readers meet is Montag. He is a fireman, and in this dystopia, that means his job is to seek out houses with books and burn both the books and the house to the ground. He loves his job, yet after he meets Clarisse and returns home to his passed-out wife, readers get the impression that Montag is not happy. He's aware that something is missing in his life, and he is curious about figuring it out. He's not a static, pyromaniac character.
Clarisse is a teenage girl who lives in Montag's neighborhood. She's a wonderful character because of how much of a quirky oddball she is. Unlike most of society, she isn't content with filling her ears with seashell sounds and staring at screens. She's lively and curious, and she's even quite blunt. It's she who asks Montag flat-out if he's happy.