Ilterish Qaghan or Ashina Qutlug (Old Turkic: 𐰃𐰠𐱅𐰼𐰾:𐰴𐰍𐰣, romanized: Elteris qaɣan, Chinese: 頡跌利施可汗/颉跌利施可汗 Xiédiēlìshīkěhàn; 阿史那骨篤祿/阿史那骨笃禄, āshǐnà gǔdǔlù, a-shih-na ku-tu-lu, d. 691) was the founder of the Second Turkic Khaganate (reigned 682–691).

Little is known about Ilterish Qaghan's early life. He was a grandson of Illig Qaghan who ruled as the final qaghan of the Eastern Turkic Khaganate. According to the Old Book of Tang, his father served as a chief under the leadership of Sheli Yuanying, the military governor of Yunzhong – a subdivision of the Chanyu Protectorate. The source specifically notes his hereditary title as that of Tutunchuo (Old Turkic: Tudun Çor). However, this is contradicted in the Chinese text inscribed on the stele dedicated to Kul Tigin, in which it is stated that Ilterish Qaghan's father bore the title of Guduolu xiejin, the Chinese rendering of Old Turkic Qutlug Irkin. This potentially suggests that the name Qutlug, borne by Ilterish Qaghan, may have represented a title inherited from his father as opposed to a personal name. Regarding Ilterish Qaghan's rank prior to his ascension as qaghan in 682, the Tonyukuk inscriptions title him as a shad – a special title given to military commanders.

Following the suppression of Ashina Funian's failed rebellion in 681, Ilterish Qaghan rose up in arms against the Tang authorities. He accumulated a military force of over 5,000 troops, partly composed of remnants of the Göktürk rebels who had served under Ashina Funian. He began his military campaigns, initially focusing on attacks against the Tang forces and the Toquz Oghuz confederation to the north.

The Tonyukuk inscriptions record that it was Tonyukuk himself and a certain Boyla Bagha Tarkan who enthroned Ilterish Qaghan. The Chinese sources expand on this, detailing that following his enthronement, Ilterish Qaghan appointed his younger brothers Mochuo as a shad, and Duoxifu as a yabghu.

His attacks on the Tang border regions began on 12 July 682, when they attacked the Lan Prefecture and captured and executed its prefect, Wang Demao. Half a year later, due to the poor climatic conditions in their headquarters, the Turks began plundering the northern borders of the Bing Prefecture. In response to these attacks, the military general Xue Rengui was assigned to defend the Yun Prefecture against Turkic aggression. This culminated in an engagement between the two military forces, resulting in the defeat of the Turks who suffered thousands of losses. However, the Turkic forces resumed their attacks, and in March 683 had plundered the Ding and Gui prefectures. The following month the Turks besieged Chanyu and killed its adjutant, Zhang Xingshi. Similarly, the prefect of the Yu Prefecture – Li Sijian – was also killed following an attack in the region by the Turks.

The military governor of the Feng Prefecture, Cui Zhibian, led an expedition against the Turks. However, this resulted in Cui Zhibian's capture by the Turks. As a result of these defeats and losses, the Tang court almost decided on abandoning the Feng Prefecture, although this did not come to fruition due to opposition from its adjutant, Tang Xiujing. Between June and July 683, the Turks began attacking the Lan Prefecture which resulted in a defeat at the hands of the assistant general Yang Xuanji who routed Ilterish Qaghan's forces. However, due to the incessant attacks on the prefecture, Emperor Gaozong and the Tang court decided to degrade the region to a lesser military institution. On 8 December 683, the commander Cheng Wuting led an expedition against the Turkic headquarters.

In 684, Ilterish Qaghan turned his attention to the steppe and initiated his campaign against the Toquz Oghuz. Following the subjugation of the Eastern Turks by the Chinese in 630, the Toquz Oghuz confederation had come to occupy and dominate Ötüken – the former heartland and symbolic centre of the Turks. As such, the ousting of the Toquz Oghuz and reconquest of Ötüken was necessary for Ilterish Qaghan to consolidate his authority and impose himself as suzerain of the steppe, and true qaghan of the Turks and steppe nomads. This campaign is detailed in the Tonyukuk inscriptions. They note that a deserter from the Toquz Oghuz informed the Turkic leaders that the qaghan of the Toquz Oghuz – Baz Qaghan (Yaoluoge Dujiezhi) – had sent letters to the Tang and Khitans, requesting to form a tripartite alliance against the expanding Turks. After learning of this, the adviser and general Tonyukuk informed Ilterish Qaghan and advised him to first attack the Toquz Oghuz. As such, the Turks expanded into Ötüken and defeated a force of 3,000 Toquz Oghuz warriors.

Following the completion of the conquest of Ötüken in 685, the Turks instigated the Toquz Oghuz in turning against the Tang government, thus initiating what the Tang perceived to be another rebellion. In response to this, the Tang dispatched around 30,000 troops from the On Oq under general Tian Yangming to subdue the Toquz Oghuz. The Toquz Oghuz tribes, primarily Uyghurs, which had surrendered to the Tang during the expedition were resettled around the citadel of Tongcheng in the Anbei Protectorate. However, tribes such as the Tongra and Pugu remained in active rebellion and thus the Tang dispatched another general, Liu Jingtong, to suppress the rebels. Due to their sheer number of losses as a result of starvation the Toquz Oghuz eventually surrendered to the Tang and were largely resettled in the Hexi Corridor, allowing for the Turks to fully dominate and resettle Ötüken.