One thing we do know for sure about Euclid is that his books, "The Elements", are the most successful in mathematical history. In fifteen books he defines modern day geometry. His textbooks were in use until the 20th century!
The Arabs of the time also thought highly of Euclid. In Arabic the name of Euclid is pronounced Uclides, which is equivalent to "key of Geometry". Euclid is geometry, now and forever.