He may have beenIranica Bahram says 'great kaqan' without giving a name. Baumer, Hist.cent.asia,2,pp99,174 says 'may have been' citing Al-Tabari who said 'highest kaghan'. Chavannes guessed 'Sogdian sub-king'. Litvinsky, hist.civs.cent.asia,iii,369 has "Ch'u-lo". Sinor, hist.inner.asia,306 has 'Ni-li' (sic), following Sebeos who said 'Great King of the Turks'. The problem is to explain why the ruler of Mongolia would leave his realm to fight in Afghanistan.
