Smart systems are evolving rapidly worldwide. Artificial intelligence (AI) provides computer systems problem-solving and decision-making features mimicking human behavior. As artificial intelligence (AI) becomes widely adopted, AI-powered systems become increasingly ubiquitous. Requirements engineering (RE) is fundamental to system development, including AI-powered systems, which provide novel RE challenges. These challenges in-clude increased need for and importance of specifying and addressing social requirements, such as responsibility, ethics, and trustworthiness; achieving a comprehensive understanding of all RE aspects, given the substantial growth in the diversity and complexity of requirements and the emergence of new and often contradictory ones; and, employing relevant methods and tech-niques that are suited for addressing these challenges. We propose an RE4AI ontology as a first step toward addressing the above challenge. The ontology provides a systematic and unambiguous representation of the accumulated RE knowledge about the system, including requirement themes, relation-ships between requirements, constraints, and stakeholders needed in the RE process. This ontology provides the basis for a complete AI RE methodology (AI-REM) framework that will incorporate methods to develop and manage AI-powered system requirements.