Assalaam Alaikum Wa Rahmatullahi Wa Barakatuh,
Bediuzzaman Said Nursi tells us the story of Dhu’l-Qarnayn in Risale-i Nur:
" According to explanations given by investigative scholars, and as indicated by the title Dhu’l-Qarnayn, names beginning with the suffix Dhu, like Dhu’l-Yazan, were used by the kings of Yemen, therefore this Dhu’l-Qarnayn was not Alexander the Great. He was rather one of the kings of Yemen who lived at the time of Abraham (UWP) and received instruction from Khidr. Alexander the Greek, however, lived approximately three hundred years before Christ, and was taught by Aristotle.
Human history goes back in regular fashion approximately three thousand years. This deficient and short view of history is not accurate concerning pre-Abrahamic times. It continues back either as superstition, or as denial, or in very abbreviated form. The reason this Dhu’l-Qarnayn of Yemen became known since early times in Qur’anic commentaries with the name Alexander, was either that it was one of his names, so that he was Alexander the Great or the Alexander of Ancient Times, or else the following:
The particular events mentioned by verses of the Qur’an are the tips of universal events. Thus, through his prophetic guidance, Alexander the Great, who was Dhu’l-Qarnayn, founded a barrier between the peoples who were oppressors and those who were oppressed, and built the famous Great Wall of China to prevent the raids of those cruel enemies. Similarly, many powerful kings and world conquerors like Alexander the Greek followed in the path of Dhu’l-Qarnayn materially, while prophets and spiritual poles, who are like the kings of man’s spiritual world, followed him in respect of spiritual matters and guidance; they built barriers between mountains-one of the most effective means of saving the oppressed from oppressors, and later constructed strongholds on mountain tops. They founded these themselves through their material power, or through their guidance and planning. Then they built walls surrounding towns and citadels inside the towns, and finally they made machine-guns and Dreadnoughts, which were like mobile citadels. The most famous barrier on earth, the Great Wall of China, covers a distance of several days’ journeying and was built to halt the incursions against the oppressed peoples of India and China of the savage tribes known in the Qur’an as Gog and Magog, and otherwise known as the Mongols and Manchurians. These tribes several times threw the world of humanity into chaos, and pouring out from behind the Himalayas wrought destruction from East to West. A long wall was built between two mountains close to the Himalayan mountains which for a long time prevented the frequent assaults of those savage peoples, and barriers were also built through the efforts of the kings of ancient Persia, who resembled Dhu’l-Qarnayn, in the mountains of Caucasia, in the region of Darband, to halt the inroads of the plundering and pillaging Tatar peoples. There are very many barriers of this sort. Since the All-Wise Qur’an speaks with all mankind, it mentions what is apparently a particular incident, recalling all events similar to it. It is from this point of view that the narrations concerning the Barrier and Gog and Magog, and the writings of the Qur’anic commentators about them, all differ."
From:
http://www.lightofquran.info/16flash.htm