In the musical, Cosette is not much of a character. She’s important to Fantine, Jean Valjean, and Marius, but she has so little personality that she’s hard to care about for her own sake – especially once she’s grown up. Cosette in the book is a different story. She’s developed more as an individual, instead of just Jean Valjean’s adopted daughter and Marius’ beloved.
Cosette is a child brought up without any love or kindness who tells lies without a second thought and spends what little free time she has chopping the heads off of flies with a toy sword. She works hard to make sure the inn always has plenty of water, knowing that if they run out, she will be sent out alone in the night to fetch more. She envies Eponine and Azelma for the simple fact that they’re allowed to be children, while she’s the same age and forced to work hard all day. Her childhood is so traumatic that she blocks it out almost completely once she grows up.
She grows into an awkward teenage girl brought up in a convent who has no knowledge of the outside world. She has received an education but has not been taught to think for herself – and yet she does anyway. She’s described as ugly, but she’s really not; she simply she pays no attention to her appearance and makes no attempt to dress fashionably. Jean Valjean arranges for them to leave the convent so that she won’t become a nun without knowing what she’s giving up. While he hopes she will choose to take her vows, she quickly sees enough of the world to know she would rather live in it than return to the convent, especially once she falls in love.
Cosette is a lot smarter than the people around her give her credit for. When she decides to start paying attention to fashion, she masters it easily. When she realizes that her father is spoiling her and neglecting himself, she convinces him to keep a fire going in his room by going to visit him frequently and gets him to eat better by promising to eat the same food as him. When Marius and Jean Valjean try to keep secrets from her, she walks right into the room and insists on joining their conversation. As she tells Jean Valjean:
“And now you must take my side against my husband … Be cross with him. Tell him I can stay here. You can talk in front of me. You must think I’m very silly. Business indeed, investing money and all that nonsense – as if it were so difficult to understand! Men make mysteries out of nothing …”
Cosette is compassionate. As a small child, she cut up flies with her toy sword for fun, but when she is older, she refuses to try to catch butterflies for fear of harming them. She is horrified when she sees a group of convicts being sent to the galleys of Toulon, the same place where Jean Valjean spent nineteen years. He assumes she would be disgusted to learn he was once one of them, but she would probably be more heartbroken for him than anything else. She is kind and gentle to everyone she encounters, even the Thenardiers, who at that point she does not remember or recognize.
She’s also braver than she seems. Even as a child, she was not afraid of the strange man in the yellow coat – Jean Valjean – and did not scream or cry when they were escaping the police together, keeping quiet as Valjean instructed her to. For a girl brought up in a convent, she is not afraid of the outside world and embraces it without losing her innocent nature. She doesn’t know what love is or what her feelings for Marius mean, but she figures it out on her own. She is not frightened to hear noises in the garden when she is left home alone, and Hugo describes her as “more like a lark than a dove”, with “a wild but courageous heart”. It’s true that she doesn’t put herself in danger the way many of the other characters do, but whenever danger is present, she faces it bravely.