Uzun Hassan (Turkish: Hassan Length) (° 1423 with Diyarbakir; † January 6th 1478) was leading Aq Qoyunlu Turkmènes. It reigned on areas of the west of the Iran, Iraq and Turkey. Its reign lasted of 1453 with 1478.

His/her grandfather Qara Yülük `Uthman Bey was named governor of Diyarbakir by Tamerlan. From there, it controlled the towns of Erzincan, Mardin, Urfa and Sivas. In 1467, Hassan overcame the leader of the Qara Qoyunlu turkmenes, Jahan Shah.

After the assassination in 1449 of the prince Astronomer Ulugh Beg of Samarkand, grandson of Tamerlan, its pupil and colleague Ali Quchtchi left with a copy the astronomical tables to which they had worked together and took refuge with Tabriz, at Uzun Hassan. This one then sent it to Istanbul, near the Othoman Sultan Mehmed II Fatih (the conqueror), where it dealt with scientific teaching with the Médersa Aya Sofia (Hagia Sophia, known as Holy-Sophie).

Uzun Hassan had seven wire: Ogurlu Mohammed, Khahil Mirza, Maksud bey, Yakub bey, Masih beg, Yusuf beg and Zegnel. In 1458, Hassan married Theodora Megale Komnena, illegitimate girl of Jean IV Comnène of the Greek Empire of Trébizonde. She was also known under the name of " Despina Hatun". Their daughter - Halime - became the mother of Chah Ismail I {{er}}, founder of the dynasty of the Séfévides. Uzun Hassan maintained good contacts with the empire of Trébizonde. When the Othoman wanted to annex the empire, it put as regards emperor. This support did not prevent the Othomans from taking Trébizonde the September 26th 1461.

His/her oldest son Ogurlu Mohammed and Maksud bey rebelled against their father, this why they were stopped then carried out. The successor of Hassan was his Yakub son.

Uzun Hassan was overcome definitively by the Othomans in 1471 with Erzincan and the August 11th 1473 with Tercan, close to Erzincan.

After a campaign against the Georgia, it fell sick and died in 1478 in its capital, Tabriz.