Johannes Nucius (also Nux, Nucis) (c. 1556 – March 25, 1620) was a German composer and music theorist of the late Renaissance and early Baroque eras. Although isolated from most of the major centers of musical activity, he was a polished composer in the style of Lassus and penned an extremely influential treatise on the rhetorical application of compositional devices.
Nucius was born in Görlitz, in Lower Silesia. He studied at the Gymnasium in Görlitz with Johannes Winckler, who was so influential in his development that he referred to him reverentially in his later writings. In 1586 he became a monk in the monastery in Rauden, in Upper Silesia; there he received a humanistic education to supplement the considerable musical training he had received under Winckler. He rose in the hierarchy at the monastery, becoming a deacon, and later an abbot at Himmelwitz; however in 1598 he turned over most of his duties to his assistants in order to compose and write his musical treatise.