**Euclid**** (ca. 325-ca. 270 BC)**

Greek geometer who wrote the *Elements*, the world's
most definitive text on geometry. The book
synthesized earlier knowledge about geometry, and was used for centuries in western Europe as a geometry textbook. The text began with
definitions, postulates ("Euclid's postulates "), and common opinions, then
proceeded to obtain results by rigorous geometric proof. Euclid
also proved what is generally known as Euclid's second theorem: the
number of primes is infinite. The
beautiful proof Euclid
gave of this theorem is still a gem and is generally acknowledged to be one of
the "classic" proofs of all times in terms of its conciseness and
clarity. In the *Elements*, Euclid used the method of
exhaustion and reductio ad absurdum. He also
discussed the so-called Euclidean algorithm for finding the greatest common divisor of two numbers, and is credited with the well-known proof of the Pythagorean theorem.

Neither the year nor place of his birth have been established, nor the
circumstances of his death, although he is known to have lived and worked in Alexandria for much of
his life. In addition, no bust which can be verified to be his likeness is
known (Tietze 1965, p. 8).

REF. http://scienceworld.wolfram.com/biography/Euclid.html