Claudius Ptolemy (/ˈtɒləmi/; Greek: Κλαύδιος Πτολεμαῖος, Klaudios Ptolemaios, pronounced*[kláwdios ptolɛmɛ́ːos]; Latin: Claudius Ptolemaeus; c. AD 90 – c. AD 168) was a Greco-Roman writer of Alexandria, known as a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology.[1][2] He lived in the city of Alexandria in the Roman province of Egypt, wrote in Greek, and held Roman citizenship.[3] Beyond that, few reliable details of his life are known. His birthplace has been given as Ptolemais Hermiou in the Thebaid in an uncorroborated statement by the 14th century astronomer Theodore Meliteniotes.[4] This is a very late attestation, however, and there is no other reason to suppose that he ever lived anywhere else than Alexandria,[4] where he died around AD 168.[5]

Ptolemy was the author of several scientific treatises, three of which were of continuing importance to later Islamic and European science. The first is the astronomical treatise now known as the Almagest (in Greek, Ἡ Μεγάλη Σύνταξις, "The Great Treatise", originally Μαθηματικὴ Σύνταξις, "Mathematical Treatise"). The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is the astrological treatise known sometimes in Greek as the Apotelesmatika (Ἀποτελεσματικά), more commonly in Greek as the Tetrabiblos (Τετράβιβλος "Four books"), and in Latin as the Quadripartitum (or four books) in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day.

Engraving of a crowned Ptolemy being guided by the muse Astronomy, from Margarita Philosophica by Gregor Reisch, 1508. Although Abu Ma'shar believed Ptolemy to be one of the Ptolemies who ruled Egypt after the conquest of Alexander the title ‘King Ptolemy’ is generally viewed as a mark of respect for Ptolemy's elevated standing in science.
The name Claudius is a Roman nomen; the fact that Ptolemy bore it indicates he lived under the Roman rule of Egypt with the privileges and political rights of Roman citizenship. It would have suited custom if the first of Ptolemy's family to become a citizen (whether he or an ancestor) took the nomen from a Roman called Claudius who was responsible for granting citizenship. If, as was common, this was the emperor, citizenship would have been granted between AD 41 and 68 (when Claudius, and then Nero, were emperors). The astronomer would also have had a praenomen, which remains unknown.

Ptolemaeus (Πτολεμαῖος – Ptolemaios) is a Greek name. It occurs once in Greek mythology, and is of Homeric form.[6] It was common among the Macedonian upper class at the time of Alexander the Great, and there were several of this name among Alexander's army, one of whom made himself King of Egypt in 323 BC: Ptolemy I Soter. All the kings after him, until Egypt became a Roman province in 30 BC, were also Ptolemies.

Perhaps for no other reason than the association of name, the 9th-century Persian astronomer Abu Ma'shar assumed Ptolemy to be a member of Egypt's royal lineage, stating that the ten kings of Egypt who followed Alexander were wise "and included Ptolemy the Wise, who composed the book of the Almagest". Abu Ma'shar recorded a belief that a different member of this royal line "composed the book on astrology and attributed it to Ptolemy". We can evidence historical confusion on this point from Abu Ma'shar's subsequent remark “It is sometimes said that the very learned man who wrote the book of astrology also wrote the book of the Almagest. The correct answer is not known”.[7] There is little evidence on the subject of Ptolemy's ancestry, apart from what can be drawn from the details of his name (see above); however, modern scholars refer to Abu Ma’shar’s account as erroneous,[8] and it is no longer doubted that the astronomer who wrote the Almagest also wrote the Tetrabiblos as its astrological counterpart.[9]

Ptolemy wrote in Greek and can be shown to have utilized Babylonian astronomical data.[10][11] He was a Roman citizen, but most scholars conclude that Ptolemy was ethnically Greek,[12][13][14] although some suggest he was a Hellenized Egyptian.[13][15][16] He was often known in later Arabic sources as "the Upper Egyptian",[17] suggesting he may have had origins in southern Egypt.[18] Later Arabic astronomers, geographers and physicists referred to him by his name in Arabic: بطليموس‎ Batlaymus.[19]