Eck, a German theologian & ordained priest, was Luther’s principal Roman Catholic opponent. He was friendly with Luther until the appearance of the Ninety-Five Theses. Ecks’ greatest achievement, the “Enchiridion” against the Lutherans, was printed in 91 editions in various languages before the year 1600.

1518 – Publishes a tract in response to Luther’s Ninety-Five Theses, calling it heretical
1519 – Eck and Luther debate at Leipzig.
1520 – Eck visits Rome, and aids in the composition of papal bull “Exsurge Domine,” which condemned 41 of Luther’s Theses and threatened him with excommunication. Pope Leo X commissions Eck to publish and enforce the papal bull throughout Germany.
1530 – Drafts a Catholic refutation of the Augsburg Confession