The first 'khagan'
402
Shelun unified the eastern steppe and made 'khagan' the supreme title. Xianbei chiefs had used the word before him; Shelun made it an emperor's, and the later Türk, Uyghur and Mongol empires inherited it.
330 – 555 AD
The Rouran (Nirun) ruled the steppe from the 330s to 555. Shelun khagan (402) was the first steppe ruler to make 'khagan' the supreme title, an older Xianbei word that every later steppe empire inherited. Their blacksmith vassals, the Türks, rose and destroyed the khaganate in 552–555.
330 is a convention. Atwood dates the state from the later fourth century, and the khaganate proper begins with Shelun's title in 402.
Mongolian historiography treats the Rouran as Mongolic-speaking: plausible but not settled. The identification of the European Avars with Rouran remnants is contested (Golden 1992; recent aDNA work).
This period has a page and its sources; the scroll-through chapter is not written yet.
402
Shelun unified the eastern steppe and made 'khagan' the supreme title. Xianbei chiefs had used the word before him; Shelun made it an emperor's, and the later Türk, Uyghur and Mongol empires inherited it.
5th century
The Rouran fought long wars against the Tuoba (Xianbei-descended) Northern Wei dynasty.
552 · the sources disagree about this
The Türks, blacksmith vassals under Bumin, revolted and crushed the Rouran in 552–555. Remnants fled west: possibly linked to the European Avars (contested).
The Avar–Rouran link is hypothesis; recent genetics offers partial support but nothing settled.