Alexander III of Macedon ( Ancient Greek : Ἀλέξανδρος , romanized : Aléxandros ; 20/21 July 356 BC – 10/11 June 323 BC), most commonly known as Alexander the Great , was king of the ancient Greek kingdom of Macedon . He succeeded his father Philip II to the throne in 336 BC at the age of 20, and spent most of his regency conducting a lengthy military campaign throughout parts of Asia and Egypt . By the age of 30, he had created one of the largest empires in history, stretching from Greece to northwestern India . He was undefeated in battle and is widely considered to be one of history's greatest and most successful military commanders.