First, there is Draco Malfoy. Draco is sometimes the leader and sometimes the clown, but either way it's because he needs the attention. He would rather people looked at him than at Harry, so it's easiest to stand next to him and stay quiet.

Draco does not start fights with anyone but Harry. He throws insults until they try to hit him, and then he uses Vincent Crabbe and Greg Goyle. They're very stupid, and like to hit people, and they've been with Draco forever. The three move as a unit, and Harry disrupts the pace whenever he walks with them.

Pansy Parkinson might be smarter than she looks. Harry thought at first that she and Draco had been betrothed since infancy, like in a fairy tale. Now he thinks they aren't, but she wants them to be. She's around enough to make it obvious, but not enough to annoy anyone too much.

There are other girls, and older students; except for the Quidditch team, all are beneath notice.

Professor Snape is the Head of House, and hates him. Harry yelled that he didn't want to be famous because his parents were dead, and Snape took points from Slytherin. Apparently he had never done that before. Draco shoves him and calls him an idiot, and has Crabbe and Goyle follow him around for a week so he doesn't get hurt too badly. Draco says that Snape thinks Harry is a bad influence. Harry thinks Snape might be a Dark wizard.

Slytherin has some classes with Gryffindor, and this is the most Harry sees of the other Houses. Hermoine Granger is smartest, and everyone pays her about as much attention as she pays them. Longbottom makes poor sport for Draco despite his shaky magic and funny last name, because he won't fight back. Harry sometimes stands up for him in Potions, because it really pisses Snape off to deduct points from Slytherin for defending Gryffindor.

Ron Weasley is the target of choice. There are four Weasley boys at Hogwarts, all with red hair and freckles, but when Draco says Weasel, he only means Ron. Ron gets mad, and very red, and fights back even when he shouldn't. Harry stays out of that. But he doesn't try to keep Draco from it, or say anything to him in front of people. They're both Slytherin, and Weasley has his own family.