The Byzantine chronicler Patriarch Nikephoros records that Toktu was "a Bulgarian, and a brother of Bayan". Although this suggests that Bayan was a man of some importance, nothing more is definitely known about Toktu's basis of support. Toktu is assumed to have been a member of that faction of the Bulgarian nobility, which advocated a hostile policy towards the Byzantine Empire. However, before Toktu managed to implement any recorded policy, he was faced with a rebellion and attempted to flee the country. Unlike his predecessor Sabin, Toktu tried to flee northwards, but was caught and killed together with his brother Bayan and their supporters near the Danube.
The 17th century Volga Bulgar compilation Ja'far Tarikh (a work of disputed authenticity) represents Azan Tokta (i.e., Toktu) as the son of the otherwise unattested Kermek, who was a son of the former Bulgarian monarch Suvar (i.e., Sevar).