If you have built Great Library in the Civilization VI: Rise and Fall ruleset, there is almost no reason to recruit Euclid. The Great Library will already give you the Eureka for Mathematics and every other Ancient and Classical technology. When another player recruits Euclid, the Great Library will give you the Eureka for another technology, which is guaranteed to be from at least the Medieval Era.
All that can be said of Euclid’s life, all that is known with a certainty, is that – according to the Greek philosopher Proclus – he taught in Alexandria during the reign of Ptolemy I, at some point between 323 and 285 BC. The “father of Geometry,” Euclid is arguably the best known mathematician of history; his 13 books of 'The Elements' were the center of teaching geometry for two millennia, and became the basis by which mathematical treatises would be judged for centuries … as much for its organization and exposition as for content.
Euclid not only set the standard by which mathematicians would forever be judged, but made rationalism the basis for all science in the modern world. His work begins with definitions and five postulates, the assumption of certain facts to serve as the basis for logical deductions. Thus the famous fifth postulate, that one and only one line can be drawn through a point parallel to a given line, formed the basis for all his proofs afterward (and when ignored, led to non-Euclidian geometry in the 19th Century). His insistence on axioms as the starting point for any investigation of a phenomenon established science as deductive, that proofs (no matter how convoluted) led to truths about existence.
The style and subject matter of the 13 books give the impression that Euclid incorporated the writings of others; this is likely true, although it is impossible to determine which parts are his and which came from others. Whatever the facts, Euclid’s own contemporaries – and mathematicians ever afterward – considered his the final and definitive word on geometry. It has been claimed that, other than the Bible, 'The Elements' is the most translated, published, and studied of all books in civilization.