Euclid of Alexandria is often called "the father of
geometry" because his text The Elements was used as
the standard geometry text for about 2000 years. It was an
excellent compilation of the mathematics known at the time
(about 350 BC), and it set an important standard for the
logical organization and presentation of mathematics.
However, it is so often associated with geometry that many
people forget three of the thirteen books of the
Elements are about number theory (books VII, VIII,
and IX). In these three books he defines prime numbers,
develops many properties of divisibility, presents the
Euclidean algorithm for finding the greatest common divisor
of two integers, shows how to find an even perfect number
from (what is now called) a Mersenne prime, proves that
there are infinitely many primes, and states a version of
the fundamental theorem of arithmetic.
Euclid's elements is one of the most widely circulated books in history. More than one thousand editions have appeared since the first printed version in 1482, and even before that it was the standard mathematical text in the west. The quality of definitions and the axiomatic development of arithmetic have greatly improved since Euclid's day, but the foundational value of Euclid's texts is difficult to overstate.
See Also: Euclid
Related pages (outside of this work)