Deontology is an ethical theory that determines morality based on adherence to rules of duty, rather than consequences. It became prominent through the work of Immanuel Kant, who argued that morality depends on acting in accordance with duty and respecting rational autonomy. Deontology holds that some actions are morally obligatory regardless of their consequences. Utilitarianism is a consequentialist theory that determines morality based on producing the greatest happiness for the greatest number of people. It focuses on outcomes rather than rules or duties.