What is "kotrag"

Kotrag (, , Kătra Pattăr) was a son of Kubrat of the Dulo clan of Bulgars. Following the death of his father, he began to extend the influence of his Bulgars up the Volga river. He is remembered as the founder of Volga Bulgaria. His successors reached the lands of modern Tatarstan and established a state during the 7th to 9th centuries which recognised Islam as the official religion in 922 AD during the visit of Baghdad khalifat ambassador Ibn Fazlan. This state remained independent until the 13th century, when it was conquered by the Batu-khan hordes of Mongolic and Turkic people widely known as Mongol-Tatars. The country's capital was called Bolghar or Great "Bulgar".