No doubt about it, Mathilde's the central character of the story. There aren't many other characters, and no one else gets anywhere near the screen time. The opening's all about Mathilde, and it's her dissatisfaction and her desires for wealth and glamour that set the plot in motion. The story's high point is her moment of happiness, and she's also the character on whom the good luck falls. She may not be the most sympathetic protagonist, but it's hard not to feel for her at least a little, especially once her life becomes genuinely tough.