I believe you confused the thread for this question. It should be, perhaps, in the "Origins of Cossacks" or in another thread.
Qazaqs/Kazakhs and Cossacks are different people although etymologically both names come from the Turkic root which means "Free men."
Taras Bulba is a fictional character invented by the Russian author Nikolai Gogol. But it is believed to be very loosely inspired by the story of Bogdan Khmelnitsky, hetman of Zaporozhian Cossacks and founder of the independent Cossack/Ukrainian state.