Euclid (Greek: Εὐκλείδης — Eukleidēs), fl. 300 BC, also known as Euclid of Alexandria and the "Father of Geometry", was a Greek mathematician of the Hellenistic period who was active in Alexandria, almost certainly during the reign of Ptolemy I (323 BC–283 BC). His Elements is the most successful textbook in the history of mathematics. In it, the principles of what is now called Euclidean geometry are deduced fro… (More on Euclid)