George Washington presided over the Constitutional Convention, whose work forms part of the founding story marked by America250.
The convention met in Philadelphia from May to September 1787. Delegates had originally been called to revise the Articles of Confederation, but they ultimately produced an entirely new framework for the federal government.
Washington was unanimously chosen to chair the convention. He generally spoke sparingly while presiding, but his reputation and leadership helped lend legitimacy to the proceedings. The completed Constitution was signed on September 17, 1787.
James Madison played a major role in preparing and recording the debates, while Benjamin Franklin was the convention's oldest delegate. Alexander Hamilton also attended and advocated a strong national government. Their important participation does not change the specific answer to who presided.