Who is Alexander the Great and what feats did he accomplish?

Alexander the Great is one of the greatest military leaders of the ancient world. He was by birth Macedonian, heir to the Macedonian kingdom, which by that time had conquered all of Greece. At the age of 20, Alexander set out on a campaign against the vast eastern empire of the Persians, during which he was able to conquer the entire territory, creating the greatest state at that time, uniting half of the world known to ancient scientists and geographers. Alexander was considered by many generals to be the greatest military leader in history.