The most important primary sources, that tell us about his life and reign, are his inscriptions, the most famous example being the trilingual inscription, in Akkadian or Babylonian, Elamite, and old Persian, carved on the Bisitun (Behistun) rock relief from the village of the same name and from his palace at Persepolis. Also, accounts about his reign were chronicled by the Greek historian Herodotus.

Darius was born in c. 550 BCE, the oldest son of Hystapes and Rhodugune. The Behistun Inscription mentions that his father occupied the position of satrap (Persian governor) of Bactria and Persis during the reign of Cyrus the Great (559-530 BCE) and his son, Cambyses (530-522 BCE). During the reign of Cambyses, Darius held the position of spearman (doryphoros) and accompanied the king in his campaign to Egypt between 528 and 525 BCE. Before leaving for Egypt, Cambyses named Patizithes as custodian of the royal palace in his absence. Patizithes saw this situation as an opportunity to gain power. He set up his own brother, Gaumata, as a false king under the name of Bardiya or Smerdis, Cambyses' brother, becoming the new ruler in 522 BCE. Cambyses II returned to his country seven months later only to find that he could not take his throne back. Some historical sources say he took his own life as he was unable to defeat the impostor king and his supporters, while other tell us he fell during the marches through Syrian Ecbatana or through Damascus.

While his various tutors' influences certainly had a profound effect upon him, Alexander seemed destined for greatness from birth. He had, first of all, a father whose accomplishments laid a firm foundation for his later success.