Claudius Ptolemy (; Greek: Klaudios Ptolemaios, Klaudios Ptolemaios [klawdios ptoleme:os]; Latin: Claudius Ptolemaeus; c. AD 100 - c. 170) was a Greco-Roman mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in the city of Alexandria in the Roman province of Egypt, wrote in Koine Greek, and held Roman citizenship. The 14th-century astronomer Theodore Meliteniotes gave his birthplace as the prominent Greek city Ptolemais Hermiou

Ptolemaeus (Ptolemaios - Ptolemaios) is a Greek name. It occurs once in Greek mythology, and is of Homeric form. 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 (Pharaohs) after him, until Egypt became a Roman province in 30 BC, were also Greek Ptolemies.  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 Roman emperors). The astronomer would also have had a praenomen, which remains unknown.  The 9th-century Persian astronomer Abu Ma'shar presents Ptolemy as 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". 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, and it is no longer doubted that the astronomer who wrote the Almagest also wrote the Tetrabiblos as its astrological counterpart.  Ptolemy wrote in Greek and can be shown to have utilized Babylonian astronomical data. He was a Roman citizen, but was ethnically either a Greek or a Hellenized Egyptian. He was often known in later Arabic sources as "the Upper Egyptian", suggesting he may have had origins in southern Egypt. Later Arabic astronomers, geographers and physicists referred to him by his name in Arabic: baTlumyws Batlamyus.

How else was the name important?
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