Gaykhatu (Mongolian: Gaikhalt; Mongolian Cyrillic: Гайхалт, died 1295) was the fifth Ilkhanate ruler in Iran. He reigned from 1291 to 1295. During his reign, Gaykhatu was a noted dissolute who was addicted to wine, women, and sodomy, according to Mirkhond. His Buddhist baghshi gave him the Tibetan name Rinchindorj.
His name means "amazing/surprising" in the Mongolian language as in "gaikhakh" (to get surprised).
He had originally been governor of Seljuk Anatolia, and was nominated for the throne by an influential Mongol commander, Ta'achar, who had murdered Gaykhatu's brother Arghun and intended to promote Baydu, but Baydu didn't show up at the quriltai, so Gaykhatu was enthroned instead. He was to care for a princess by the name of Koekecin. Gaykhatu's wife, Padshah Hatun, was the daughter of Kitlugh Turkan (Turkan Khatun) and Kirman. Padshah took the title Safwad al dunya wa al-Din (literally, Purity of the earthly world and of the faith) after Djalal da-Din Abu'l-Muzzafar was deposed as head of the Mongol tribe, who reigned in southeastern Iran. Padshah was known for killing her stepbrother, Suyurghatamish, but one of his clansmen, Khurdudjin, managed to avenge her by putting her to death with permission from Baydu during his reign as Ilkhan.
In 1292, Gaykhatu sent a message to the Egyptian Mamluk Sultan Al-Ashraf Khalil threatening him that if he not allow him to live in Aleppo he would conquer the whole of the Levant. Al-Ashraf replied: "The khan has the same ideas as me. I too hope to bring back Baghdad to the fold of Islam as previously. We will see which of us two will be quicker".
Royal extravagance 
Gaykhatu is known to have spent government money in an extravagant way. Among his beneficiaries were the Nestorian Christians, who praise him abundantly for his gifts to the Church, as apparent in the history of Mar Yahballaha III.
Introduction of paper money 
In 1294, Gaykhatu wanted to replenish his treasury emptied by royal extravagance and a great cattle plague. In response, his vizier Ahmed al-Khalidi proposed the introduction of a recent Chinese invention called Chao (paper money). Gaykhatu agreed and called for Kublai Khan's ambassador Bolad in Tabriz. After the ambassador showed how the system worked, Gaykhatu printed banknotes which imitated the Chinese ones so closely that they even had Chinese words printed on them. The Muslim confession of faith was printed on the banknotes to placate local sentiment.
The plan was to get his subjects to use only paper money, and allow Gaykhatu to control the treasury. The experiment was a complete failure, as the people and merchants refused to accept the banknotes. Soon, bazaar riots broke out, economic activities came to a standstill, and the Persian historian Rashid ud-din speaks even of "'the ruin of Basra' which ensued upon the emission of the new money". Gaykhatu had no choice but to withdraw the use of paper money.
He was assassinated shortly after that, strangled by a bowstring so as to avoid bloodshed. His cousin Baydu, another puppet placed by Ta'achar, succeeded Gaykhatu but only lasted a few months before himself being assassinated. An alternative story of Gaykhatu's death claims Baydu made war on him because of his introduction of paper money and subsequently killed him in battle.
- Stevens, John. The history of Persia. Containing, the lives and memorable actions of its kings from the first erecting of that monarchy to this time; an exact Description of all its Dominions; a curious Account of India, China, Tartary, Kermon, Arabia, Nixabur, and the Islands of Ceylon and Timor; as also of all Cities occasionally mention'd, as Schiras, Samarkand, Bokara, &c. Manners and Customs of those People, Persian Worshippers of Fire; Plants, Beasts, Product, and Trade. With many instructive and pleasant digressions, being remarkable Stories or Passages, occasionally occurring, as Strange Burials; Burning of the Dead; Liquors of several Countries; Hunting; Fishing; Practice of Physick; famous Physicians in the East; Actions of Tamerlan, &c. To which is added, an abridgment of the lives of the kings of Harmuz, or Ormuz. The Persian history written in Arabick, by Mirkond, a famous Eastern Author that of Ormuz, by Torunxa, King of that Island, both of them translated into Spanish, by Antony Teixeira, who liv'd several Years in Persia and India; and now render'd into English.
- Atwood, p. 234
- Al-Maqrizi, p.242/vol.2
- Luisetto, p.146
- Ashtor 1976, p. 257.
- Steppes, p. 377
- Atwood, Christopher P. (2004). The Encyclopedia of Mongolia and the Mongol Empire. Facts on File, Inc. ISBN 0-8160-4671-9.
- René Grousset, Empire of the Steppes: A History of Central Asia, 1939
- Luisetto, Frédéric, "Arméniens et autres Chrétiens d'Orient sous la domination Mongole", Geuthner, 2007, ISBN 978-2-7053-3791-9