The Greco-Roman name Dionysius, deriving from the name of the god Dionysos or Dionysus, was exceedingly common, and many ancient people, famous and otherwise, bore it. It remains a common name today in the form Dennis (Denys, Denis).

Among the historical figures known by the name Dionysius, some of the more famous were:

• Dionysius the Elder (or Dionysius I), a ruler of Syracuse in Sicily
• Dionysius the Younger , (or Dionysius II), son of the preceding, more famous than his father, the quintessential Graeco-Roman tyrant
• Dionysius Periegetes, Greek geographer, 3d century BC
• Dionysius Thrax, Greek grammarian, 2d century BC
• Dionysius the Areopagite, a citizen of Corinth who was converted by Paul of Tarsus
• Dionysius of Halicarnassus, a Greek historian of the Roman period
• Saint Dionysius of Alexandria, an Egyptian bishop of the 3d century
• Saint Denis, Bishop of Paris, martyr (died ca. 250)
• Pope Dionysius
• Pseudo-Dionysius the Areopagite, identified by some with a Georgian theologist Peter the Iberian (411‑491), author of Corpus Areopagiticum
• Dionysius Exiguus, a Dacian monk who helped set the date of some Christian holidays
• Dionysius Telmaharensis, a former head of the Syrian Jacobite Church
• Dionysius the Wise, the Russian medieval icon-painter
• Dionysius I, Metropolitan of Moscow, a 14th century orthodox prelate
• Benjamin Musaphia, Jewish doctor, scholar, and kabbalist (1606-1675), who sometimes called himself Dionysius.
• Dionysius Lardner, an Irish scientific writer