theologian and mystic, one of the important contributors to, and propagators of, the influential school of Rhenish spirituality originating in the 14th century.

Educated at the University of Cologne, Dionysius entered the Carthusian order at the charterhouse of Roermond, in 1425. In 1451–52 he accompanied Nicholas of Cusa, papal legate to northern Germany and the Netherlands, on a mission for church reform in the Rhineland. In charge of the Carthusians at 's Hertogenbosch from 1465, he retired in 1469 because of poor health.

The school of Rhenish spirituality was influenced by Neoplatonism, the theology of St. Thomas Aquinas, and the teaching of Pseudo-Dionysius, whose works especially inspired late medieval mystics. Dionysius used Aquinas, Pseudo-Dionysius, and the Dutch mystic Jan van Ruysbroeck as principal authorities in writing his classic, De contemplatione. For Dionysius, mystical contemplation was an infusion of the gift of wisdom by the Holy Spirit, for which the soul could be prepared by the renunciation of all save God. A prolific writer on dogmatic, ascetical, and mystical theology, he also sent letters to rulers calling for a crusade against the Turks, wrote treatises on church reformation, and compiled commentaries on Scripture and Pseudo-Dionysius, a compendium on Aquinas' Summa, and a handbook of philosophy. His commentaries and treatises were particularly popular in the 16th century. Dionysius' Opera Omnia were published (1896–1935) in 42 volumes.