The UN Charter describes him or her merely as the “chief administrative officer of the organization,” yet today the Secretary-General is widely recognized as the UN’s chief political representative. How did this transformation and expansion of the office from administrative to political take place? Existing scholarship tends to emphasize the contribution made by Dag Hammarskjöld. This article challenges that story on two accounts: first, by pointing out the importance of institutional factors and not just the officeholder’s personality; and second, by examining the contribution made by Trygve Lie, the UN’s first Secretary-General. The article establishes a conceptual framework based on institutional theory to understand the role of the Secretary-General and analyzes Lie’s contribution in the period 1946-1953.