Evincing leadership from the moment of his arrival in Western Maryland, Hager quickly became a leading citizen. He was involved in many activities: farmer, cattleman, even a gunsmith. Hager was a volunteer Captain of Scouts during the French and Indian War. In 1762 he founded Hagerstown and in 1771 and 1773 he was elected to the General Assembly at Annapolis, qualifying him as the first German to make his mark in politics.
On November 6,1775, Captain Hager was accidentally killed while supervising the building of the German (now Zion) Reformed Church on land which he had donated. At the time, he was serving on various critical pre-Revolutionary War Committees. Hager has been called the "Father of Washington County" due to his having laid the groundwork for its separation from Frederick County in 1776 and the subsequent creation of Hagerstown as County.