The longest-serving Prime Minister of the United Kingdom was Sir Robert Walpole, who served from 1721 to 1742. While the title "Prime Minister" was not formally established until later, Walpole is recognized for his leadership during this period, effectively functioning as the head of government. His tenure is marked by a strong influence over Parliament and efforts to stabilize the country after previous conflict. Walpole's legacy includes establishing practices of coalition-building and political management that continue to impact the role of Prime Minister today.