Kaykaus ibn Kaykhusraw or Kayka'us II (Persian: عز الدين كيكاوس بن كيخسرو, ʿIzz ad-Dīn Kaykāwus ibn Kaykhusraw) was the sultan of the Seljuqs of Rûm from 1246 until 1262.^[1]

Kaykaus was the eldest of three sons of Kaykhusraw II. His mother was Prodoulia, who was a Byzantine Greek, may have had Kaykaus baptized as a child.^[2][3] He was a youth at the time of his father's death in 1246 and could do little to prevent the Mongol conquest of Anatolia. For most of his tenure as the Seljuq Sultan of Rûm, he shared the throne with one or both of his brothers, Kilij Arslan IV and Kayqubad II. Mongol commander Baiju threatened him and warned him of being late with paying tribute and requested new pastures in Anatolia for the Mongol cavalry. The Mongols defeated Kaykaus who then fled to the Roman empire in 1256/1257.^[4] At some point, Kakykaus returned to the Sultanate but had to again flee to Byzantium following civil war with Kiliji Arslan IV around the summer of 1262, this time accompanied by his family.^[5] The Roman court detained him, though, they welcomed him as usual. Soon however tensions grew between Sultan and Emperor, and Kaykaus tried to depose Michael.^[5] So Kaykaus's brother Kayqubad appealed to Berke Khan of the Golden Horde. Nogai invaded the Empire in 1265 and released him and his men after Emperor Michael VIII Palaiologos detained an envoy from Cairo to Berke. Berke gave Kaykaus appanage in Crimea and had him married to his daughter, Urbay Khatun.^[6] He died an exile in 1279 or 1280 in Crimea.

According to Rustam Shukurov, Kaykaus II "had dual Christian and Muslim identity, an identity which was further complicated by dual Turkic/Persian and Greek ethnic identity".^[7] Kaykaus and his sons were all said to be baptised, and whilst in Constantinople the family visited church baths, received communion and attended Easter services under the watch of the Patriarch Arsenios.^[3] Even when in Crimea, Kaykaus still insisted on his Christian faith, defending Arsenios against charges of noncanonical communication with pagans (Kaykaus and his family) by asking for the engolpion he'd left in Constantinople and offering to eat pork to prove his orthodoxy.^[8]

Kaykaus had multiple wives, but only one accompanied him to Byzantium. The Armenian Kirakos Gandzaketsi reported that Kaykaus was married to a daughter of the emperor John III Doukas Vatatzes and later Ottoman sources give her name as Anna, however both of these claims are unreliable and likely only indicate that his wife was Christian and possibly Roman. This wife continued to live in Constantinople following Kaykaus' escape.^[9]

Kakyaus' children, all with unknown mothers were:

• Ghiyāth al-Dīn Masʿūd (b.1262-1308), the eldest son and heir who accompanied Kaykaus to Byzantium and then to the Golden Horde. Following Kaykaus' death, Masʿūd reclaimed his father's position, becoming the last Sultan of Rum, and maintained good relations with Michael VIII's son Andronikos II Palaiologos.^[10]
• Rukn al-Dīn Kayūmarth (b.1262- a.1293), the middle son who also followed his father to Byzantium and the Golden Horde. Involved in a power struggle with Masʿūd following Kaykaus' death that ended in Kayūmarth's imprisonment and death.^[11]
• Constantine Melik (b.1264- a.1306), who stayed in Constantinople after Kaykaus' escape, likely owing to his young age. Constantine remained in Roman service for the rest of his life and had an illustrious career as governor of Berroia in the 1280s and then of Pegai in 1305/1306. Constantine was at some point given the title of Caesar or Sebastokrator, and his descendants continued to serve in the Roman empire till its collapse in the 15th century.^[12]
• Sabbas Soultan? (b.1265-1320?), another son who stayed behind in Constantinople. He appears to have become a monk and served under the Patriarch of Constantinople before moving to Crimea where he died.^[13]
• Unnamed daughter (b.1264-?), who was arrested after her father's escape.^[14]
• Rukn al-Dīn Qılıc Arslan (a.1264-?), one of the sons of Kaykaus born in Crimea after the flight from Constantinple.^[14]
• Siyāwus (a.1264-?), one of the sons of Kaykaus born in Crimea after the flight from Constantinple.^[14]
• Farāmarz (a.1264-?), one of the sons of Kaykaus born in Crimea after the flight from Constantinple.^[14]

Though deposed and exiled, Kaykaus remained popular among the Turkmen of Anatolia and a threat to the stability of the fragile Seljuq-Mongol relationship. The vizier Fakhr al-Din Ali was imprisoned for a time in 1271 for corresponding with him. It was from Kaykaus that Karamanoğlu Mehmed Bey in 1276 sought help in his uprising against the Mongols. Since Kaykaus was in no position to help, Mehmed Bey thought it best to have a representative of Kaykaus’ line on his side, even if only an imposter, and named Jimri as head of the revolt. Kaykaus later dispatched several of his sons from the Crimea as pretenders, one of which, Masud II, was ultimately successful in winning the Seljuq throne in 1280.

Some modern historians consider the Byzantine noble Athanasios Soultanos to have been the brother or son of Kaykaus, but this is unlikely due to the later age Soultanos lived in. However another branch of the Christianized aristocratic family of the Soultanoi was indeed begun by a close relative of Kaykaus, whence their name.^[15]

In the Ottoman period the rebel Sheikh Bedreddin, who drew support largely from Turkmen migrants to the Balkans, claimed descent from Kaykaus II.

• Anatolian Seljuks family tree

• Cahen, Claude (1968). Pre-Ottoman Turkey: a general survey of the material and spiritual culture and history. Translated by J. Jones-Williams. New York: Taplinger. pp. 271–279.
• de Nicola, Bruno (2017). Women in Mongol Iran: the Khātūns, 1206-1335. Edinburgh: Edinburgh University Press. ISBN 978-1474415484.
• Peacock, A.C.S.; Yildiz, Sara Nur, eds. (2013). The Seljuks of Anatolia: Court and Society in the Medieval Middle East. I.B.Tauris. ISBN 978-0857733467.
• Shukurov, Rustam (2016). The Byzantine Turks, 1204-1461. BRILL. ISBN 9789004307759.

• Prof. Dr. Mehmet Eti. "Anatolian Coins > Seljuqs of Rum > Kay-Ka'us II first reign". Archived from the original on 2008-02-01.
• Prof. Dr. Mehmet Eti. "Anatolian Coins > Seljuqs of Rum > Kay-Ka'us II second reign". Archived from the original on 2008-02-01.