Khlesl, Melchior a German theologian, born at Vienna in 1553 of Protestant parents, was induced to enter the Roman Catholic Church, and joined the Jesuits. After studying five years under the Jesuits he took the first four orders, then continued his studies for two years at Ingolstadt, and was ordained priest in 1579. He became successively provost of the cathedral at Vienna, administrator of the bishopric of Neustadt in 1588, and bishop of Vienna in 1598. The loose conduct of the Roman Catholic clergy having greatly contributed to the rapid spreading of Protestant doctrines, Khlesl showed himself a zealous partisan of reform in this respect, while, on the other hand, he did his utmost to bring Protestants back into the fold of Romanism. Yet he was still more inclined to mingle in politics than in Church affairs. He attached himself to the grand duke Matthias, eldest brother of the emperor Rudolph II, whom the latter particularly disliked on account of a prediction, according to which this brother was to depose him. The emperor contemplated exiling Khlesl, but the latter succeeded in organizing a conspiracy, and Matthias was made emperor in Rudolph's place. The Protestant princes had a part in this revolution, but Khlesl took good care that they should not derive any benefit from it to further their religion. Under emperor Matthias he became president of the privy council in 1611, and cardinal in 1616. Notwithstanding his opposition to Protestantism, which he rigorously persecuted in 1616-18, he remained at the head of the German party, and opposed the adoption of the grand duke Ferdinand as heir to the throne. Ferdinand himself by arresting Khlesl at Vienna, July 20, 1618, and confining him first at the castle of Ambras, and then at the convent of Georgenberg, in Tyrol. In 1622 a requisition from the pope caused him to be transferred to Rome, where he was imprisoned for seven months in the castle of St. Angelo. After his liberation he returned to Vienna in 1627, and was restored to the possession of his property and his offices. He gave up politics to attend exclusively to the management of ecclesiastical affairs, and died Sept. 18, 1630. His fortune, amounting to over half a million, he left to the bishopric of Vienna; 100,000 florins to Neustadt and Vienna for a yearly mass for his soul; 100,000 florins to the convent of Himmelspforte, 20,000 to the Jesuits, and 46,000 to his relatives. Khlesl's motto was " Strong and mild:" strong in action, mild in manner; the latter was somewhat difficult for him to submit to, as he was naturally hasty. He had not received a classical education, but was well versed in the Bible, in patristics, and in homiletics. See Hammer-
Purgstall, Lebensbeschreibung des Cardinals Khlesl (Vienna, 1847-51,4 vols. 8vo) ; Pierer, Univ. Lex. s.v.; Wetzer und Welte, Kirch.-Lex. 6:225.