Dionysius the Areopagite (Greek Διονύσιος ὁ Ἀρεοπαγίτης) was a judge of the Areopagus who, as related in the Acts of the Apostles, (Acts 17:34), was converted to Christianity by the preaching of the Apostle Paul. According to Dionysius of Corinth, quoted by Eusebius, this Dionysius then became the second Bishop of Athens.
In the early 6th century, a series of famous writings of a mystical nature, employing Neoplatonic language to elucidate Christian theological and mystical ideas, was ascribed to the Areopagite. They have long been recognized as pseudepigrapha and are now attributed to "Pseudo-Dionysius the Areopagite".
Dionysius was also popularly mis-identified with the martyr of Gaul, Dionysius, the first Bishop of Paris, Saint Denis.
In the Eastern Orthodox Church, Dionysius the Areopagite and Saint Denis of Paris are celebrated as one commemoration on 3 October.
On pages 190 and 191 of Owen Gingerich's monograph on Copernicus The Book Nobody Read, reference is made to an astronomical fresco in the main gallery of the Escorial Library, near Madrid, Spain, built 1567-84, which shows Dionysius the Areopagite observing an eclipse at the time of Christ's crucifixion. In a footnote Gingerich mentions that an eclipse (of the sun by the moon) couldn't have happened at that time because Passover is a full moon event, and solar eclipses always happen at new moon.
The legend is based on a claim made by Pseudo-Dionysius in a letter addressed to Polycarp: "What have you to say about the solar eclipse which occurred when the Savior was put on the cross? At the time the two of us were in Heliopolis and we both witnessed the extraordinary phenomenon of the moon hiding the sun at the time that was out of season for their coming together... We saw the moon begin to hide the sun from the east, travel across to the other side of the sun, and return on its path so that the hiding and the restoration of the light did not take place in the same direction but rather in diametrically opposite directions..."
Pseudo-Dionysius had apparently read the Alexandrinus variant of Lk 23:44f where the darkness said to have accompanied the crucifiction is attributed to an eclipse.
In 1457 the Italian humanist Lorenzo Valla wrote: "...the claim of 'Dionysius'... that he observed the eclipse of the sun at the hour of the Saviour's death... is as blatant a fiction as the epistolary form of the report." 
A Christian writer, called Areopagīta, from his having been a member of the court of Areopagus at Athens. He was converted to Christianity by St. Paul's preaching (Acts, xvii. 34). He is reported to have been the first bishop of Athens, being appointed to that office by the apostle Paul, and to have suffered martyrdom under Domitian. His fundamental thought is the absolute transcendence of God. During the Middle Ages a great number of writings were circulated under his name, and were collected together and printed at Cologne in 1536, and subsequently at Antwerp in 1634 and at Paris in 1646. They have now, for a long time, been deemed spurious, although scholars differ in respect to the times and authors of the fabrication. The most probable reasoning, however, fixes them at the end of the fourth century. The standard text is that of Corderius, reprinted by the Abbé Migne. Trans. by Parker (1894). See Harnack's Dogmengeschichte, vol. ii., and the studies by Niemeyer (1869) and Schneider (1884).