Gilbert
This 24 year old is under way too much pressure in his family, and he feels trapped in his obligations and in the small town where he lives. He longs to be free from the burdens of his family, but not because he doesn't love them. He is the primary caretaker of his family, although Amy is the emotional leader of the home.
Arnie
Arnie is a mentally handicapped boy who was born with serious birth defects which the doctors predicted would kill him before he turned 10. The novel takes place as Arnie approaches his 18th birthday. The family is often worried that Arnie will threaten his health or safety, and he often does. He is frustrating in other ways too, and ultimately, Gilbert attacks Arnie, but they love each other a lot, and they make peace, but Arnie is still hurt. Arnie is a loving kid who acts out when he's not the center of attention.
Gilbert's mom
Gilbert's mom was left horrified and depressed after the untimely suicide of her husband. She began overeating and by the novel's beginning, she has become so overweight that it seems she could die at any moment too. She is so overweight that Gilbert has to go into the basement where his father hanged himself in order to fix the floor where she sits—her weight has weakened the floorboards. In the end, her weight kills her, but not before her prayers are answered: she gets to see Arnie turn 18.
Amy
Amy is the emotional center of the family. She is the peacemaker who coordinates between frustrated siblings who are lonely and sad and who often fight with each other. Amy is also lonely and sad, especially because she wishes they could all be one big happy family again.
Ellen
Ellen is younger than Amy, and Amy's childhood was less painful than Ellen's, so the two often butt heads. Ellen is sexually active it seems, but she is just barely a teenager. She is a good person with a nasty temper and a ruthless cynicism from her disappointing relationship to her mother and the tragic absence of her father.
Janice
Janice is a minor character in the story. She was old enough to leave when everything happened with her father, so although she and Gilbert (and Amy) were able to help with the family, Janice escaped to a rewarding life, and Gilbert is jealous that she travels the world while he stays in a dying town in the middle of nowhere.
Larry
Larry moved away too, but he comes back with Janice for Arnie's 18th birthday party. Larry doesn't come home much because it is too painful to bear; he was the son who found their father's hanging body, and the horrifying sight left him with PTSD. Coming home and seeing the house is too difficult, so he stays away.
Becky
Becky is young, but she's intelligent and mature. Gilbert knows that she is not eligible for true romance, but they still hang out and it's pretty obvious that they are attracted to each other. So obvious that Mrs. Carver (Gilbert's affair) becomes jealous.
Mrs. Carver
Mrs. Carver is not so subtle these days about her relationship with Gilbert. Sometimes he feels that she is risky on purpose because she wants to get caught, but that just leaves her husband jealous and suspicious. Gilbert dodges his confrontations until one day, Mr. Carver has a heart attack and dies, and Mrs. Carver leaves town forever.
