Charlie Kelmeckis
Charlie is the central character in the movie and much more complex than we at first imagine. From childhood, he has suffered from depression and at the start of the film has just been released from a mental healthcare facility. He is ready to go back to a mainstream school but he does not feel as ready as his doctors tell him that he is. Charlie is socially withdrawn and not very good at making friends which is why kids his own age tend to pick on him.
He is fortunate that two older kids, Patrick and Sam, take him under their wing and introduce him to a social life he could never have found for himself. He feels confident in their friendship and even begins to confide in them, telling Sam that his best friend died the year before. Charlie has seen a lot of emotional trauma for a young man his age and does not know how to deal with it. He bottles things up to avoid dealing with them. However they tend to come back on their own anyway and he begins to get flashbacks about his aunt's death when he was seven years old; Aunt Helen was killed in a car accident on the way to celebrate his birthday, which also happens to be Christmas Eve. At first the flashbacks are brief and can be pushed out of his consciousness but eventually they become too much for him to bear.
When Sam touches his inner thigh in a moment of intimacy, Charlie suffers another far worst flashback. He is unable to cope with the emergence of repressed memories that triggered his emotional and mental spiral in the first place; his Aunt Helen was abusing him sexually when he was a child. He feels guilty and ashamed of this and also guilty because he thinks her car crash was his fault, since he spent a lot of time wishing her dead whilst she was abusing him.
By the end of the film, Charlie's story is almost a hopeful one. He has learned how to cope with his memories and feelings; he is in love with Sam (although she is leaving for college) and he has some friends. He has learned how to live and feel comfortable with that.
Patrick
Patrick is Charlie's first friend in high school, and although it's not stated, he is running a little behind the curve in some of his school subjects - he is the only senior in Charlie's freshman shop class. He is an open and very friendly young man and he is the catalyst for Charlie becoming a part of their group of friends. He has a happy home life and is well-balanced, getting along incredibly well with his step-sister Sam. He is comfortable with his own sexuality; Patrick is gay and involved in a relationship with high school football star Brad. Although there is a temporary break in the friendship between Charlie and the group, it is ultimately healed when Charlie sticks up for Patrick after he is beaten up for being gay. Their friendship is very genuine and lasting.
Sam
Sam is Patrick's step-sister and also his very close friend. She is a friendly and open girl who is in a relationship with another student named Craig. Charlie falls in love with her immediately. At the beginning of the film we are not sure if she feels the same way about him as he does about her, but when she tells him that his first kiss should be with someone who actually loves him, and then kisses him, we begin to realize that there is some attraction there, even though the love could equally be platonic between good friends at this stage. Later, Sam instigates further intimacy which he shies away from when she touches his inner thigh and triggers his memories of his aunt abusing him.
Sam is accepted to Penn State and at the end of the novel leaves for school, returning when she hears that Charlie has suffered a mental breakdown. She is a true and loyal friend.
Mary Elizabeth
Mary Elizabeth is Charlie's first girlfriend and is part of the group of friends that he is welcomed into. When Charlie acts as a stand-in date for Sam, Mary Elizabeth thinks this is so sweet that she wants to be his girlfriend and asks him to take her to an upcoming dance. When they kiss afterwards, she declares that he is her boyfriend. This is a little awkward because Charlie really has no interest in her or feelings for her beyond friendship, but he has never broken up with anyone before and so she remains his girlfriend by default. Their relationship comes to an end after a game of Truth or Dare during which Charlie is dared to kiss the prettiest girl in the room and he kisses Sam instead of his own girlfriend.
Brad
Brad is the archetypal jock, and the star of his high school football team. Slightly less archetypically jock-ish is his sexuality; he is involved in a relationship with Patrick, but he is less comfortable with this situation than Patrick is because he is afraid of his father's reaction and therefore wants to keep their relationship a secret. This works well for a while but when his father walks in on his son and Patrick having sex, he punches Brad in the face, and he goes to school the following day sporting bruises, and also with a changed attitude towards his former boyfriend. Brad becomes very cruel towards Patrick, and snubs him, calling him a faggot in the school cafeteria which eggs his friends on to beat Patrick up until Charlie intervenes.
Mr Anderson
Mr Anderson is Charlie's favorite teacher, and a person with whom he seems able to make a bond that is almost a friendship. Because Charlie wants to be a writer, a bond with his English teacher makes sense, and Mr Anderson is non-judgmental, trying to get Charlie to open up a little.
Aunt Helen
Aunt Helen was killed in a car accident when Charlie was seven years old. He was traumatized by this and it has always been thought that his flashbacks and reaction to the trauma are entirely to do with the fact that he lost his favorite aunt whilst she was driving to his home to bring him a birthday gift, thereby making him feel guilty, and at his young age, unable to process this guilt.
However, the truth turns out to be much darker because Helen was sexually abusing her nephew from his earliest years, and when Charlie pulls away from Sam in their intimate moments, it is because she touches his thigh in the same way that Aunt Helen had in his early childhood.
Charlie's Parents
Mr and Mrs Kelmeckis are loving and involved parents who have done everything they can to help their son work through his depression even though they don't really understand its source or cause. They were absolutely unaware that his aunt was abusing him.
Craig
Craig is Sam's high school boyfriend, of whom Charlie is extremely jealous. She eventually breaks up with him when she learns he has been cheating on her.
Dr Burton
Dr Burton is the mental healthcare professional who discovers that Charlie was sexually abused and is the doctor who is able to begin to heal him.
