Prior to his conquest of Siberia, Yermak's combat experience consisted of leading a Cossack detachment for the tsar in the Livonian War of 1558-83 and plundering merchant ships. Based on legends and folk songs, for years, Yermak had been involved in robbing and plundering on the Volga with the hetman Ivan Kolzo and four other Cossack leaders. Historian Valerie Kivelson refers to Yermak's group as “his gang of thugs.” Like many other Cossacks, Yermak's gang was involved in the “thieves” trade ["“vorovskim” remeslom"]. It was typical of Cossacks to engage in piracy on the Sea of Azov or the Caspian Sea and to rob various envoys and Russian or Persian merchants. Though a bandit, Yermak earned a reputation as an eminent and loyal Russian fighter. Through his experience fighting in the Livonian War, he learned war tactics and excelled beyond the other hetmans in skill.