Euclid Euclid Euclid (; – "Eukleídēs", ; fl. 300 BC), sometimes given the name Euclid of Alexandria to distinguish him from Euclides of Megara, was a Greek mathematician, often referred to as the "founder of geometry" or the "father of geometry". He was active in Alexandria during the reign of Ptolemy I (323–283 BC). His "Elements" is one of the most influential works in the history of mathematics, serving as the main textbook for teaching mathematics (especially geometry) from the time of its publication until the late 19th or early 20th century. In the "Elements", Euclid deduced the theorems of what
Ptolemy Ptolemy Claudius Ptolemy (; , "Klaúdios Ptolemaîos" ; ; ) was a Greco-Roman mathematician, astronomer, geographer and astrologer. 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 () in the Thebaid (). This attestation is quite late, however, and, according to Gerald Toomer, the translator of his "Almagest" into English, there is no reason to suppose he ever lived anywhere other than Alexandria. He died there around AD 168. Ptolemy wrote several scientific