The earliest extant mention of the term is for a ruler of the North Caucasian Huns in the 680s, referred to in Christian sources from Caucasian Albania as Alp Ilutuer. The title was also mentioned in Letter to Kültegin in 732. It was used by rulers of pre-Islamic Volga Bulgaria during the period of their vassalage to the Khazars.
Rásonyi (1942:92), apud Golden (1980:149), glossed an "il teber" as "one who steps on the il at the head of conquered tribes"; with il descending from Proto-Turkic *ēl "realm" (Clauson, 1972:121; Sevortijan, 1974:339) whereas täbär from Turkic root *täp- "to kick with foot" (or *tep- / *dēp- "to stamp, tramp"). However, Erdal (2007:81-82) objects to Rásonyi's proposal: Erdal points out that "the Orkhon Turkic aorist of täp- would be täpär" and instead suggests a non-Turkic origin for the title. Róna-Tas (2016:72–73) proposes an Iranian etymology; he compares the Turkic title (H)elteber to Manichean Bactrianl’dβr, Written Sogdianδātβar, Sogdian ryttpyr / dyttpyr (*litbir), etc. from Middle Iranian *lātbär < Old Iranian *dāta-bara "who brings the law", ultimately from Proto-Indo-European roots *dʰēH "to put, place" & bʰer- "to bring", respectively.
Kevin Alan Brook. The Jews of Khazaria. 3rd ed. Rowman & Littlefield Publishers, 2018.
Gerard Clauson. “él:”, in An Etymological Dictionary of Pre-Thirteenth-Century Turkish, Oxford: Clarendon Press, 1972.
Douglas M. Dunlop. The History of the Jewish Khazars, Princeton, N.J.: Princeton University Press, 1954.
Marcel Erdal, "The Khazar Language" in The World of the Khazars. Brill, 2007. pp. 75–108.
Peter B. Golden. Khazar Studies: An Historico-Philological Inquiry into the Origins of the Khazars. Budapest: Akadémiai Kiadó, 1980.
Norman Golb and Omeljan Pritsak, Khazarian Hebrew Documents of the Tenth Century. Ithaca: Cornell University Press, 1982.
András Róna-Tas, "Bayan and Asparuχ. Nine Notes on Turks and Iranians in East Europe", in Éva Á. Csató et al.(ed.), Turks and Iranians. Interactions in Language and History.The Gunnar Jarring Memorial Program at the Swedish Collegium for Advanced Study. (Turcologica, Vol. 105), Harrassowitz, Wiesbaden 2016, ISBN 978-3-447-10537-8, pp. 65–78.
Ervand Sevortjan. Etymological Dictionary of Turkic Languages (in Russian), volume 1, Moscow: Nauka, 1974.