Final answer:
A hetman (or ataman) was a Cossack leader, responsible for both military and civil administration within Cossack territories.
Step-by-step explanation:
The term hetman (or ataman) refers to the historical title given to the leaders of the Cossacks. Therefore, the correct answer to the question 'What was a hetman (or ataman)?' is c. Cossack leader. The role of the hetman was not limited to military command but also included civil administration within the territories controlled by the Cossacks. Consequently, choices such as 'ambassador from German-speaking lands', 'member of the tsar's advisory council', and 'Tatar leader' do not accurately describe the position of a hetman. In the context of Eastern Europe, particularly in the history of Ukraine and the Cossack Hetmanate, a hetman or ataman was a military leader or chieftain of the Cossacks. The Cossacks were semi-military communities known for their skill in warfare and their role in the defense of the frontier regions of the Russian and Ottoman Empires. The hetman held a significant position of authority within the Cossack social and military structure.