Dhul-Qarnayn (Zul Qarnain)

(Arabic ذو القرنين  literally "He of the Two Horns" or "He of the two centuries" is a figure mentioned in the Qur'an, the sacred scripture of Islam, where he is described as a great and righteous ruler who built a long wall that keeps Gog and Magog from attacking the people who he met on his journey to the east (i.e., the rising of the sun). According to a classical interpretation, the name is due to his having reached the two 'Horns' of the Sun, east and west, where it rises and where it sets" during his
journey. The identification of Dhul-Qarnayn in historical context is not clear, and therefore this subject has generated various theories. In modern scholarship the character is usually identified as Alexander the Great, who is ascribed similar adventures in the Alexander romance. The same opinion is held in traditional Islamic scholarship. In other modern scholarship the character is usually identified as Cyrus the Great Some modern scholars also identify the character as Byzantine emperor Heraclius, who was celebrated by his contemporaries as a "second Alexander" and whose Persian campaign had inspired the Alexander romance.

The story of Dhul-Qarnayn appears in sixteen verses of the Qur'an, specifically verses 18:83-98:

Verse	Yusuf Ali	Pickthall
18:83	They ask thee concerning Zul-qarnain Say, "I will rehearse to you something of his story."	They will ask thee of Dhu'l-Qarneyn. Say: "I shall recite unto you a remembrance of him."
18:84	Verily We established his power on earth, and We gave him the ways and the means to all ends.	Lo! We made him strong in the land and gave him unto every thing a road.
18:85	One (such) way he followed,	And he followed a road
18:86	Until, when he reached the setting of the sun, he found it set in a spring of murky water: near it he found a people: We said: "O Zul-qarnain! (thou hast authority), either to punish them, or to treat them with kindness."	Till, when he reached the setting-place of the sun, he found it setting in a muddy spring, and found a people thereabout. We said: "O Dhu'l-Qarneyn! Either punish or show them kindness."
18:87	He said: "Whoever doth wrong, him shall we punish; then shall he be sent back to his Lord; and He will punish him with a punishment unheard-of (before).	He said: "As for him who doeth wrong, we shall punish him, and then he will be brought back unto his Lord, Who will punish him with awful punishment!"
18:88	"But whoever believes, and works righteousness, he shall have a goodly reward, and easy will be his task as we order it by our command."	"But as for him who believeth and doeth right, good will be his reward, and We shall speak unto him a mild command."
18:89	Then followed he (another) way.	Then he followed a road
18:90	Until, when he came to the rising of the sun, he found it rising on a people for whom We had provided no covering protection against the sun.	Till, when he reached the rising-place of the sun, he found it rising on a people for whom We had appointed no shelter therefrom.
18:91	(He left them) as they were: We completely understood what was before him.	So (it was). And We knew all concerning him.
18:92	Then followed he (another) way.	Then he followed a road
18:93	Until, when he reached (a tract) between two mountains, he found, beneath them, a people who scarcely understood a word.	Till, when he came between the two mountains, he found upon their hither side a folk that scarce could understand a saying.
18:94	They said: "O Zul-qarnain! the Gog and Magog (people) do great mischief on earth: shall we then render thee tribute in order that thou mightest erect a barrier between us and them?"	They said: "O Dhu'l-Qarneyn! Lo! Gog and Magog are spoiling the land. So may we pay thee tribute on condition that thou set a barrier between us and them?"
18:95	He said: "(The power) in which my Lord has established me is better (than tribute): help me therefore with strength (and labour): I will erect a strong barrier between you and them:	He said: "That wherein my Lord hath established me is better (than your tribute). Do but help me with strength (of men), I will set between you and them a bank."
18:96	"Bring me blocks of iron." At length, when he had filled up the space between the two steep mountain sides, he said, "Blow (with your bellows)" then, when he had made it (red) as fire, he said: "Bring me, that I may pour over it, molten lead."	"Give me pieces of iron" - till, when he had leveled up (the gap) between the cliffs, he said: "Blow!" - till, when he had made it a fire, he said: "Bring me molten copper to pour thereon."
18:97	Thus were they made powerless to scale it or to dig through it.	And (Gog and Magog) were not able to surmount, nor could they pierce (it).
18:98	He said: "This is a mercy from my Lord: but when the promise of my Lord comes to pass, He will make it into dust; and the promise of my Lord is true."	He said: "This is a mercy from my Lord; but when the promise of my Lord cometh to pass, He will lay it low, for the promise of my Lord is true."

Traditional exegesis (tafsir)

According to Tafsir ibn Kathir by Ibn Kathir, a widely used 14th-century commentary on the Qur'an:

The Quraysh sent An-Nadr bin Al-Harith and `Uqbah bin Abi Mu`it to the rabbis in Al-Madinah, and told them: `Ask them (the rabbis) about Muhammad, and describe him to them, and tell them what he is saying. They are the people of the first Book, and they have more knowledge of the Prophets than we do.' So they set out and when they reached Al-Madinah, they asked the rabbis about the Messenger of Allah. They described him to them and told them some of what he had said. They said, `You are the people of the Tawrah and we have come to you so that you can tell us about this companion of ours.' They (the rabbis) said, `Ask him about three things which we will tell you to ask, and if he answers them then he is a Prophet who has been sent (by Allah); if he does not, then he is saying things that are not true, in which case how you will deal with him will be up to you. Ask him about some young men in ancient times, what was their story for theirs is a strange and wondrous tale. Ask him about a man who travelled a great deal and reached the east and the west of the earth. What was his story And ask him about the Ruh (soul or spirit) – what is it If he tells you about these things, then he is a Prophet, so follow him, but if he does not tell you, then he is a man who is making things up, so deal with him as you see fit.

According to Maududi's conservative 20th century commentary:

This Surah was sent down in answer to the three questions which the mushriks of Makkah, in consultation with the people of the Book, had put to the Holy Prophet in order to test him. These were: (1) Who were "the Sleepers of the Cave"? (2) What is the real story of Khidr? and (3) What do you know about Dhul-Qarnain? As these three questions and the stories involved concerned the history of the Christians and the Jews, and were unknown in Hijaz, a choice of these was made to test whether the Holy Prophet possessed any source of the knowledge of the hidden and unseen things. Allah, however, not only gave a complete answer to their questions but also employed the three stories to the disadvantage of the opponents of Islam in the conflict that was going on at that time at Makkah between Islam and un-belief.