Short answers, pulled from the story.
The first contact between the Pannonian Avars and the Byzantine Empire occurred in 557 when an embassy arrived in Constantinople from the northern Caucasus. This delegation represented a coalition of Eurasian nomads seeking to escape the rule of the Göktürks.
Genetic studies confirm that elite Pannonian Avars possessed Ancient Northeast Asian ancestry with paternal lineages such as N1a1a1a1a3a-F4205 and Q-M242. While early samples showed high levels of East Asian origin, later periods revealed significant mixing with local European populations.
Khagan Bayan I had established supremacy over most Slavic, Germanic and Bulgar tribes living in Pannonia and the Carpathian Basin by about 580. He commanded an army of 10,000 Kutrigur Bulgars who sacked Dalmatia in 568.
The Frankish campaigns against the Pannonian Avars began in 788 and ended with the surrender of chieftains in 796 after disease killed most horses. The submission of all Pannonia was recorded in Annales Regni Francorum beginning in 796.
The language spoken by the Pannonian Avars remains unknown despite extensive scholarly investigation into their history. Historians have proposed origins from Mongolian, Turkic, Tungusic, Iranian, or Proto-Slavic languages based on titles and loanwords found in records.