William Faulkner described Caddy Compson as the true hero of The Sound and the Fury. However, the reader's image of her is mediated through the narrative voices of her three brothers: Benjy in part 1 of the novel, Quentin in part 2, and Jason in part 3.
Benjy's section of the novel is the least clear. Caddy takes care of him like a mother, but he also sees her as a child. He remembers when Caddy climbed a tree, and he looked up and noticed that her underclothes were muddy. This is symbolic of the sexual impurity which Quentin condemns more explicitly.
Quentin is protective of Caddy's honor and is horrified by her promiscuity. He has old-fashioned romantic ideals of chivalry and purity and wants to protect his sister from sin and from criticism. At one stage, he claims to have committed incest with her in a strange attempt to share in the consequences of what he regards as her sin. His obsession with Caddy grows as his mental state deteriorates, propelling him towards suicide.
Jason is the most straightforward of the three brothers and also is the crudest. He sees Caddy in her social role as a mother and attempts to make money out of her care for her daughter, assuming the role of her guardian and stealing the money Caddy sends for her upkeep. For him alone among the brothers, Caddy's sexual conduct is of little more than practical interest.