The full title of Behn's novella is Oroonoko, or The Royal Slave: A True History. "The Royal Slave" is an oxymoron, reflecting core contradictions at the heart of Oroonoko.
First and foremost, Behn's audience at the time—literate citizens of the British Empire, likely also members of the aristocracy—would have considered royalty and slavery mutually exclusive. The ability to enslave another person is a function of power. The white ruling classes in England exerted their powers as "royalty" to exploit, colonize, and enslave millions of people like Oroonoko. The phrase "royal slave" is an oxymoron because the oppressed and the oppressor, the victim and the perpetrator coexist within the same statement.
These contradictions are rife within Oroonoko: a man who perpetrates prisoner-of-war slavery in his own country while himself falling victim to the transatlantic slave trade. Behn's white aristocratic readership would undoubtedly have perceived Oroonoko as "less human" had they met him. Behn goes to great lengths to contradict this, portraying Oroonoko at every turn as a man whose morality, honor, intellect, and courage far surpass that of anyone in his country, rivaling that of the classic heroes and gods of antiquity. An objection to chattel slavery on the basis of a single man's exceptional qualities does not an abolitionist argument make. However, though Behn does not seek to undermine the aristocracy's oppressive power, she does weave a narrative that invites her readers to question common stereotypes of enslaved people.