 Born Johann Möller to a family of Lutheran German burghers, he entered the Russian artillery in 1739 as a rank private, and by 1752 had been commissioned as an officer.By 1759 he was a lieutenant-colonel, and saw action in the Seven Years' War.At the Siege of Kolberg in 1761 he gained distinction as commander of the artillery under Rumyantsev, and was later entrusted with organizing and commanding one of the army's first light infantry units.