Dr. Mikhail Cossack is a brilliant scientist who became the main antagonist in Mega Man 4.
He sent a letter to Dr. Light challenging Mega Man to defeat his Robot Masters, claiming that he would prove to the world that he was the greatest robotic scientist in the world. After defeating Cossack's robots, Mega Man rushes to Cossack's citadel in Siberia, where he meet the doctor and fights him. However, before Mega Man could defeat him, Proto Man interrupts the battle, along with Cossack's daughter, Kalinka, who was kidnapped by Dr. Wily. Wily was using Cossack for his mad schemes. After Wily is defeated, Cossack befriends Dr. Light and makes Mega Man a pet bird robot named Beat as a gift for defeating Wily again.