Klesl or Khlesl, Melchior (both: mĕlˈkhyôr klāˈsəl) [key], 1552–1630, Austrian politician, cardinal of the Roman Catholic Church. The son of a Protestant baker, he was converted to Catholicism by the Jesuits and became chancellor of the Univ. of Vienna. Made (1581) an official of the bishop of Passau and then (1598) bishop of Vienna, he led the campaign to drive Protestantism from Lower Austria. Later, however, as adviser to Archduke (after 1612, Holy Roman Emperor) Matthias, he concluded that only a policy of compromise would preserve intact the Hapsburg domains. In 1615 he was created cardinal. Archduke Ferdinand (later Holy Roman Emperor Ferdinand II), attributing the emperor's delay in putting down the Prague insurrection (the prelude to the Thirty Years War) to Klesl's influence, had him imprisoned (1618). Later released (1622) and transferred to Rome, he returned to Vienna as bishop in 1627.