Who is Dhul-Qarnayn in the Quran?

Mostly, we know him only from the Quran: a righteous, powerful ruler who travelled east and west and built a barrier against Gog and Magog. The Quran never gives his real name, era or homeland, and scholars have suggested several identities. What matters most is the lesson: power used with faith, justice and humility.

What the Quran says about him

His story is in Surah al-Kahf. Allah tells the Prophet ﷺ: "They ask you about Dhul-Qarnayn. Say, 'I will relate to you something of his narrative'", and says He established him in the land and gave him the means to all things (Quran 18:83-84). The name Dhul-Qarnayn means "the one with two horns" (or "two ages"), and the Quran doesn't explain it.

His three journeys

West: he reached the place where the sun seemed to set in murky water and found a people there. He was told to punish or treat them kindly (Quran 18:85-86). He said that whoever does wrong would be punished, and whoever believes and does good would have the finest reward and easy commands (Quran 18:87-88).
East: he reached the place where the sun rises and found a people with no shelter from it (Quran 18:90).
Between two mountains: he found people who begged for protection from Gog and Magog, who were spreading corruption. They offered to pay him, but he refused payment, saying what his Lord had given him was better, and asked only for their help to build a barrier (Quran 18:93-95).

Gog and Magog (Ya'juj and Ma'juj) have their own article. See Who are Gog and Magog in Islam?

His humility

After building the barrier, he did not boast. He gave the credit to Allah and acknowledged that it, too, would one day end:

قَالَ هَـٰذَا رَحْمَةٌ مِّن رَّبِّى ۖ فَإِذَا جَآءَ وَعْدُ رَبِّى جَعَلَهُۥ دَكَّآءَ ۖ وَكَانَ وَعْدُ رَبِّى حَقًّا "He declared, 'This is a mercy from my Lord. But when the promise of my Lord comes to pass, He will level it to the ground. And my Lord's promise is ever true.'" Quran 18:98

Who was he?

The Quran does not say, so scholars have offered different ideas. Some have suggested Alexander the Great, although others object because Alexander is not known to have been a believer in One God. Some classical scholars thought he was a righteous king from an earlier age, perhaps from Yemen. Some modern writers have proposed Cyrus the Great of Persia. None of these is certain, and Muslims are not required to choose one. The Quran leaves his identity out because the lesson does not depend on it.

Lessons from his story

Power is a trust from Allah, to be used for justice and to help the weak.
He declined payment for protecting people and asked only for their help.
Success comes from effort and faith together: he asked the people to help him build.
Remain humble, because everything made by humans ends one day.

This story is one of four in Surah al-Kahf, which many Muslims read on Fridays. See Should I read Surah al-Kahf on Fridays? The same surah tells of the young believers in the cave. See What is the story of the People of the Cave?

Key points

Dhul-Qarnayn is a righteous ruler mentioned in Surah al-Kahf (verses 83-98).
The Quran does not name him or say when he lived.
He travelled west and east and built a barrier against Gog and Magog.
The lesson is justice, service and humility in power.

Tip: When you read this section of Surah al-Kahf, ask yourself what "means to all things" Allah has given you, such as time, skills or influence, and how to use them well.