Euclid of Megara, founder of the Megarian (also called the eristic or dialectic) school of philosophy, was born c. 450 BC, probably at Megara, though Gela in Sicily has also been named as his birthplace (Diogenes Laërtius ii. 106), and died in 374. He was one of the most devoted of the disciples of Socrates. Aulus Gellius (vi. 10) states that, when a decree was passed forbidding the Megarians to enter Athens, he regularly visited his master by night in the disguise of a woman; and he was one of the little band of intimate friends who listened to the last discourse. He withdrew subsequently with a number of fellow disciples to Megara, and it has been conjectured, though there is no direct evidence, that this was the period of Plato’s residence in Megara, of which indications appear in the Theaetetus. He is said to have written six dialogues, of which only the titles have been preserved.

Euclid of Megara is not the Euclid who wrote The Elements, though, on occasion, he has been called such.

From the eleventh edition of The Encyclopedia, 1911. Public domain. Some editing has been done for the sake of clarity.