Despite the moral underpinnings of Karl Popper’s philosophy, he has not presented a well-established moral theory for critical rationalism (CR). This paper addresses the ontological status of _moral agents_ as part of a research program for developing a moral theory for CR. It argues that moral agents are _selves_ who have achieved the cognitive capacity of _personhood_ through an evolutionary scenario and interaction with the environment. This proposal draws on Popper’s theory of the self and his theory of three worlds, (...) which offer both epistemological and ontological insights into the emergence and evolution of _moral agents_. The paper also discusses some of the consequences of this proposal for the _objectivity_ and _criticizability_ of moral judgments and the moral agency of artificial intelligence. It concludes by suggesting some directions for future research on the epistemological and ontological problems of ethics in CR. (shrink)