The article reveals the conceptual foundations of the formation of the modern theory of the subject of law on the basis of the achievements that were made in this area during the Soviet period. The main attention is paid to the analysis of A.V. Mickiewicz's teaching about the subject of law. It is emphasized that the scientist inextricably linked the understanding of the subject of law with the concept of legal personality and its structure. He considered social relations to be the leading determinant of the subject of law, bringing to the fore in the theory of the subject of law not the personal, but the social aspect. The ideas of A.V. Mickiewicz are compared with the corresponding ideas of S.N. Bratusya, as well as other researchers. It is emphasized that in modern conditions, the development of the doctrine of subjects of law is influenced by the principles of post-non-classical scientific rationality with its inherent anthropocentrism. It is also noted that the theory of the subject of law is actualized by modern technological development, primarily digital and bio-technologies. It is concluded that the teaching of A.V. Mickiewicz about the subject of law retains its relevance at the present stage of the development of legal science.