17-year-old Jack “Mass” Masselin is a popular, “jock”-type junior at Martin Van Buren High School who serves as one of the novel’s two main characters. Readers learn much about Jack’s physical traits when he remarks on his reflection in the bathroom mirror: “The guy in the mirror isn’t bad-looking—high cheekbones, strong jaw, a mouth that’s hitched up at one corner like he just got done telling a joke […] like he’s smart and he knows he’s smart” (30). Jack seems to acknowledge his own arrogance, perhaps even embracing it, at least early in the novel. Readers gain further insight into his personality in his apology letter to Libby, where he writes that he considers himself “charming” and “hilarious,” “the life of the party” (16). Based on other characters’ interactions with him—especially other popular students like Dave Kaminski, Seth Powell, and the beautiful Caroline Lushamp—Jack appears to carry quite a bit of status at the school and is initially highly motivated to preserve it.

Below the surface, however, Jack is a complicated and conflicted protagonist: he suffers from a rare and debilitating condition called prosopagnosia, which is “an inability to recognize the faces of familiar people, typically as a result of damage to the brain” (18).