Eratosthenes, a Greek mathematician from the 3rd century BC, developed a simple sieve method for identifying prime numbers. The method works by sieving out multiples of successive numbers, leaving the prime numbers behind. It involves making a list of consecutive numbers up to a certain number, crossing out numbers that are multiples of 2, then crossing out multiples of 3, and so on, leaving the remaining uncrossed numbers as the prime numbers. The document then proceeds to explain Eratosthenes' sieve method in more detail through 5 steps.