Euclid was a Greek mathematician who developed a theorem that was later named in his honor as the Euclidean Algorithm. He developed a version of the fundamental theorem of arithmetic, and he showed that no finite collection of primes contains them all.
Euclid wrote "Elements," a collection of 13 books comprised of geometrical theorems. The "Elements" defined the mathematical terms number, prime number, composite and perfect number. Euclid proved a sequence of theorems that marks the beginning of number theory as a mathematical endeavor versus a numerological one. Euclid's third contribution remains one of the most elegant proofs in mathematics.