Greek astronomer, geographer, philosopher and mathematician who, at 30 years of age, was appointed chief librarian of the Library of Alexandria by the pharaoh Ptolemy III.
Eratosthenes (c. 276 BCE – c. 194 BCE)
He is credited with having calculated the circumference of the Earth with an error of less than 1%, which is quite accurate for his time. He also developed a method called the “sieve of Eratosthenes” to determine the sequence of prime numbers.