1503-1559. Roman Catholic theologian. Born in Soest, Westphalia, he studied in Cologne, and his chief activities were in the service of Hermann von Wied,* archbishop of Cologne. At the provincial synod in 1536, Gropper's reform program did not receive approval. In 1538, together with the canons of the Cologne council, he published a handbook of Christian doctrine which contained an exposition of the Decalogue, the Creed, and the seven sacraments. At the Colloquies of Hagenau and Worms (1540-41) he took a mediating position between Roman Catholics and Lutherans, setting forth the doctrine of double justification (justness by faith and justness by love), in which he evidenced the influence of Erasmus. His Liber Ratisbonesis became the basis of negotiations at the Colloquy of Ratisbon* (1541). However, he prevented Hermann von Wied from carrying through the Protestantization of Cologne as advocated in the Consultatio by and . Gropper participated in the , especially the third and fifth sessions (1546) and the thirteenth and fifteenth sessions (1551-52). He declined the appointment as cardinal by Paul IV.