The Constitution was written by several committees over the summer of 1787, but the committee most responsible for the final form we know today is the "Committee of Stile and Arrangement". This Committee was tasked with getting all of the articles and clauses agreed to by the Convention and putting them into a logical order. On September 10, 1787, the Committee of Style set to work, and two days later, it presented the Convention with its final draft. Heading the draft was the Preamble. The members were Alexander Hamilton, William Johnson, Rufus King, James Madison, and Gouverneur Morris. The actual text of the Preamble and of much of the rest of this final draft is usually attributed to Gouverneur Morris. The newly minted document began with a grand flourish - the Preamble, the Constitution's r'aison d'etre.
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.