Hulagu Khan (also known as Hülegü, and Hulegu) (1217 – 8 February 1265) was a Mongol ruler who conquered much of Southwest Asia. The grandson of Genghis Khan and the brother of Arik Boke, Mongke and Kublai Khan, he became the first khan of the Ilkhanate of Persia.

Hulagu, the child of Tolui and Sorghaghtani Beki, a Christian woman, was dispatched by his brother Mongke in 1255 to accomplish the destruction of the remaining Muslim states in southwestern Asia. First, the subjugation of the Lurs, a people of southern Iran; second, the destruction of the sect of the Assassins; third, the destruction of the Abbasid caliphate; and lastly, the destruction of the Ayyubid states in Syria and the Mamluk state in Egypt.

Hulagu marched out with perhaps the largest Mongol army ever assembled. Hulagu easily destroyed the Lurs, and his reputation so frightened the Assassins that they surrendered their impregnable fortress of Alamut to him without a fight.

Hulagu probably always intended to take Baghdad, which the Mongols had been meaning to attack for over ten years (see Eljigidei), but he used the caliph's refusal to send troops to him as a pretext for conquest. Hulagu sent a message to the caliph, Al-Musta'sim, containing the following (trans. John Woods):

"When I lead my army against Baghdad in anger, whether you hide in heaven or in earth

I will bring you down from the spinning spheres;

I will toss you in the air like a lion.

I will leave no one alive in your realm;

I will burn your city, your land, your self.

If you wish to spare yourself and your venerable family, give heed to my advice with the ear of intelligence. If you do not, you will see what God has willed."

The caliph was not sure how to react to Hulagu's invasion, but weakly defended the city. Hulagu ordered various sections of Baghdad's population spared, such as learned men and Christians, but killed at least 250,000 people (contemporary sources say 800,000). Hulagu killed the caliph by wrapping him in a rug and having him either "beaten to a pulp" or trampled by horses. Marco Polo reports that Hulagu starved the caliph to death, but there is no corroborating evidence for that.

Thus was the caliphate destroyed, and Iraq ravaged—it has never again been such a major center of culture and influence. The smaller states in the region hastened to reassure Hulagu of their loyalty, and the Mongols turned to Syria in 1259, conquering the Ayyubids and sending advance patrols as far head as Gaza. Egypt's turn seemed next, but the death of Mongke forced Hulagu and most of his army to withdraw, for the succession crisis that followed was the most ruinous to date.

In the meantime, the Mongols had fallen out with the crusaders holding the coast of Palestine, and the Mamluks were able to ally with them, pass through their territory, and destroy the Mongol army at the Battle of Ain Jalut. Palestine and Syria were permanently lost, the border remaining the Tigris for the duration of Hulagu's dynasty.

Hulagu returned to his lands by 1262, but instead of being able to avenge his defeats, was drawn into civil war with Batu Khan's brother Berke, suffering severe defeat in an attempted invasion north of the Caucasus in 1263. He died in 1265 and was buried in the Kaboudi Island in Lake Urmia. He was succeeded by his son Abaqa, thus establishing his line.