Roo is Olive's sometimes-lover, a working man who spends most of the year in the fields performing manual labor. He is a member of an older class of men, preferring to work with his hands instead of pursuing higher education, learning, or business; this gives him an air of rugged masculinity, despite his obvious devotion to Olive. The text describes him in a fairly complete manner:
ROO: Pleased to meet yer. (Smiles slowly at her and PEARL relaxes a little. He is a man's man with a streak of gentleness, a mixture that invites confidence... recent experiences have etched a faint line of bewilderment between his eyes, a sign of the first serious mental struggle he has ever had in his life...
(Lawler, Summer of the Seventeenth Doll, Google Books)
Roo is a member of the Australian "bush," the collective of working men who see each other as "mates," people with a personal connection deeper than family. His connection to the working class makes it hard for him to fit in with Olive and her upper-class friends; however, harsh economic times have forced Roo to abandon his mates and work in the city. In his inner heart, Roo believes that he will marry Olive and live in happiness; in reality, his actions and their shared deceits prevent them from ever reaching that romantic end. Roo discovers that he cannot compete with the city, and similarly cannot compete with the younger generation.