Dutch Reformed theologian (1603-1669) and principal architect of seventeenth-century Reformed covenant theology in its developed form. Born Johannes Cock at Bremen; trained at the Bremen Gymnasium and at Hamburg, Franeker, and Leiden in classical languages, Hebrew, and theology; appointed professor of biblical philology at Bremen (1630), then professor of Hebrew at Franeker (1636), then professor of theology at Franeker (1643), then professor of theology at Leiden (1650-1669). Cocceius's principal contribution is the systematic development of Reformed covenant theology in its mature seventeenth-century form. His foundational work Summa Doctrinae de Foedere et Testamento Dei (Sum of the Doctrine of the Covenant and Testament of God, 1648) articulated the redemptive-historical structure of biblical theology through the lens of the covenant of works (with Adam in the Garden, requiring obedient performance) and the covenant of grace (with the elect in Christ, requiring faith). His extensive biblical commentary work (eight Old Testament volumes, four New Testament volumes, with substantial Hebrew exegetical depth) applied this covenant framework throughout the Bible. Cocceius's biblical-redemptive-historical approach was sometimes in tension with the more strictly scholastic-deductive approach of Gisbertus Voetius at Utrecht; the resulting Cocceian-Voetian controversies dominated Dutch Reformed academic theology in the 1650s and 1660s. Both Cocceius and Voetius were thoroughly Reformed; the tension was over method and emphasis, not over the substantive doctrines. The patriarchal-Reformed reader values Cocceius as the architect of mature Reformed covenant theology whose work undergirds subsequent federal-theological development (Witsius, Owen on the covenants, the broader Puritan covenant tradition, Vos's biblical theology).