Mahmud Ghazan (also Ghazan Khan, sometimes westernized as Casanus; 5 November 1271 – 11 May 1304) was the seventh ruler of the Ilkhanate from 1295 to 1304, division of the Mongol Empire based in modern-day Iran. He was the son of Arghun, grandson of Abaqa Khan and great-grandson of Hulegu Khan, continuing a long line of rulers who were direct descendants of Genghis Khan. Considered the most prominent of the Ilkhans, he is perhaps best known for converting to Islam and meeting Imam Ibn Taymiyya in 1295 when he took the throne, marking a turning point for the dominant religion of the Mongols in West Asia.
One of his many principal wives was Kököchin, a Mongol princess (originally betrothed to Ghazan's father Arghun before his death) sent by his great-uncle Kublai Khan.
Military conflicts during Ghazan's reign included war with the Mamluk Sultanate for control of Syria and battles with the Turko-Mongol Chagatai Khanate. Ghazan also pursued diplomatic contacts with Europe, continuing his predecessors' unsuccessful attempts at forming a Franco-Mongol alliance. A man of high culture, Ghazan spoke multiple languages, had many hobbies, and reformed many elements of the Ilkhanate, especially in the matter of standardizing currency and fiscal policy.
Ghazan's parents were Arghun and his concubine Kultak Egechi of the Dörböd. At the time of their marriage, Arghun was 12. Kultak's elder sister Ashlun was the wife of Tübshin, son of Hulagu and the previous viceroy in Greater Khorasan. According to Rashid al-Din Hamadani, the marriage took place in Mazandaran, where Arghun was viceroy.
Ghazan was born on 5 November 1271 in Abaskun (now near Bandar Torkaman), although he was raised in the nomadic palace of the orda of his grandfather Abaqa's favorite wife, Buluqhan Khatun, who herself was childless. Ghazan and Arghun didn't see each other until Abaqa's attack on Qara'unas in 1279, when they briefly met.
Ghazan was raised an Eastern Christian, as was his brother Öljaitü. The Mongols were traditionally tolerant of multiple religions, and during Ghazan's youth, he was educated by a Chinese Buddhist monk, who taught him Old Mandarin and Buddhism, as well as the Mongolian and Uighur scripts.
He lived together with Gaykhatu in Buluqhan Khatun's encampment in Baghdad after Abaqa's death. He reunited again with his father when Buluqhan Khatun was wed to Arghun and became Ghazan's step-mother.
After the overthrow of Tekuder in 1284, Ghazan's father Arghun was enthroned as Ilkhan, the 11-year-old Ghazan became viceroy, and he moved to the capital of Khorasan, never to see Arghun again. Emir Tegene was appointed as his deputy, who he didn't like very much. In 1289, conflict with other Mongols ensued when a revolt was led against Arghun by Nawruz, a young emir of the Oirat clan, whose father had been civil governor of Persia before the arrival of Hulegu. Ghazan's deputy Tegene was among the victims of Nawruz's raid on 20 April 1289 in which he was captured and imprisoned. Nawruz's protege, Prince Hulachu was arrested by Ghazan's commander Mulay ten days later. When Nawruz was defeated by Arghun's reinforcements in 1290, he fled the Ilkhanate and joined the alliance of Kaidu, another descendant of Genghis Khan who was the ruler of both the House of Ögedei and the neighboring Chagatai Khanate. Ghazan spent the next ten years defending the frontier of the Ilkhanate against incursions by the Chagatai Khanate of Central Asia.
When his father, Arghun, died in 1291, Ghazan was prevented from pursuing his claim of leadership in the capital because he was engaged both with Nawruz's raids, and dealing with rebellion and famine in Khorasan and Nishapur. Taghachar, an army commander who had served the previous three generations of Ilkhans, was probably behind the death of Arghun, and supported Ghazan's uncle Gaykhatu as the new Ilkhan. Despite being boyhood rivals, Gaykhatu sent aid to Ghazan's fight against Nawruz in Khorasan under the leadership of Prince Anbarchi (son of Möngke Temür) and emirs Tuladai, Quncuqbal and El Temür; himself going to Anatolia to quell Turcoman uprisings. However, famine reached his court too in spring and Anbarchi, unable to feed his soldiers, had to leave soon for Azerbaijan again. He again tried to visit Gaykhatu, but after his refusal, he had to go back. Ghazan received Kököchin, a Mongol princess from the Yuan dynasty in China, on his way back from Tabriz to Khorasan. She had been brought from the east in a caravan which included Marco Polo among hundreds of other travellers. She had originally been betrothed to Ghazan's father, IlKhan Arghun, but since he had died during her months-long journey, she instead married his son Ghazan.
In 1294, Ghazan forced Nawruz to surrender at Nishapur and Nawruz then became one of Ghazan's lieutenants. Ghazan was loyal to his uncle, though he refused to follow Gaykhatu's lead in introducing paper currency to his province, explaining that the weather of Khorasan was too humid to handle paper.
In 1295, Taghachar and his conspirators, who probably had been behind the death of Arghun, had his successor Gaykhatu killed as well. They then placed the pliable Baydu, a cousin of Ghazan, on the throne. Baydu was primarily a figurehead, allowing the conspirators to divide the Ilkhanate among themselves. Hearing of Gaykhatu's murder, Ghazan marched on Baydu. Baydu explained that Ghazan was away during the events leading to Gaykhatu's fall, therefore nobles had no choice but to raise him to throne. Nevertheless, Nawruz encouraged Ghazan to take steps against Baydu, because he was nothing but a figurehead under grips of nobles. Baydu's forces commanded by Ildar (his cousin and Prince Ajay's son), Eljidei and Chichak met him near Qazvin. Ghazan's army were commanded by Prince Sogai (son of Yoshmut), Buralghi, Nawruz, Qutluqshah and Nurin Aqa. The first battle was won by Ghazan but he had to fall back after realising that Ildar's contingent was just a fraction of the whole army he faced, leaving Nawruz behind. Nevertheless, he captured Arslan, a descendant of Jochi Qasar.
After a short truce, Baydu offered Ghazan co-rulership of the Ilkhanate and offered Nawruz the post of sahib-i divan to which as a counter-condition Ghazan demanded the revenues of his father's hereditary lands in Fars, Persian Iraq and Kerman. Nawruz refused these conditions, which led to his arrest. According to an anecdote, he promised to bring Ghazan back tied up on condition of his release. Once he reached Ghazan, he sent back a cauldron to Baydu; a word play on the Turkish word kazan. Nawruz promised him the throne and his help on condition of Ghazan's conversion to Islam. Ghazan converted to Sunni Islam, on June 16, 1295, at the hands of Ibrahim ibn Muhammad ibn al-Mu'ayyid ibn Hamaweyh al-Khurasani al-Juwayni as a condition for Nawruz's military support.
Before converting to Islam based on a political agreement, Ghazan, a neo-Muslim, married his stepmother Bulughan Khatun Muazzema after his father's death, in accordance with the Mongol pagan Yasa customs. After being informed that it was forbidden by Islamic law, he ignored it and broke the agreement by leaving Islam, leading to the massacre of Syrian Muslims and the conversion of millions of neo-Muslim Tatars in his kingdom to their former religion. In order to dissuade him from doing so, some jurists, considering Maslaha, temporarily considered the marriage legal and encouraged him to remain in Islam, thus saving him from the great harm of Muslim genocide and apostasy and giving Ghazan a long time and opportunity to realize his mistake, so he remained in Islam.
Nawruz entered Qazvin with 4,000 soldiers and claimed an additional number of 120,000 soldiers commanded by Ebügen (in other sources, 30,000) – descendant of Jochi Qasar – on his way towards Azerbaijan which caused panic among masses which was followed by defections of Taghachar's subordinates (thanks to Taghachar's vizier Sadr ul-Din Zanjani) and other powerful emirs like Qurumishi and Chupan on 28 August 1295.