The father of geometry is almost a complete mystery as a person
Euclid's Elements dominated geometry for more than two thousand years, until the early 19th century. Yet nobody knows when he was born, and nearly everything about his life comes from writers centuries later. For ages scholars even confused him with a different Euclid, a pupil of Socrates.
Euclid was a Greek geometer and logician active around 300 BC, usually ranked with Archimedes and Apollonius of Perga among antiquity's greatest mathematicians. Four of his treatises survive largely intact: the Elements, Optics, Data and Phaenomena. Beyond that, little is certain. The standard story rests on Proclus, writing in the 5th century AD, who placed him under Ptolemy I, after Plato's followers and before Archimedes. Some scholars guess a birth around 330 or 325 BC; others decline to guess.
He probably worked in Alexandria, the city Alexander the Great founded in 331 BC. Pappus reports that Apollonius studied with Euclid's students there, which suggests Euclid founded a mathematical tradition in the city. Speculation has him trained at Plato's Academy, bridging Athenian and Alexandrian mathematics. Medieval Arabic sources supply a detailed life, claiming he was born in Tyre and lived in Damascus, but these accounts are unverifiable and widely doubted. Byzantine and early Renaissance writers mixed him up with Euclid of Megara.
The Elements, in thirteen books, is more than geometry. It covers plane geometry, basic number theory and solid geometry, with books on proportion and irrational lines fitting awkwardly into that scheme. Book 1 opens with 20 definitions and then 10 assumptions, five postulates and five common notions, from which theorems are deduced step by step. Much of the material came from predecessors such as Eudoxus, Theaetetus and Hippocrates of Chios; Euclid's achievement was the synthesis and the rigorous structure.
The name means something like son of renown, from Greek roots for well and fame. In English it can stand for his book or even for geometry itself. He also wrote on perspective, conic sections and spherical geometry, and many of his works are lost, while his authorship of a few surviving titles is questioned.
Source: Euclid
