Who was the first President of the United States?

George Washington, and the most consequential thing he did was stop. He was elected unopposed, could have stayed indefinitely, and stepped down after two terms - which set a precedent that held for 150 years without any law requiring it, until Franklin Roosevelt broke it and it was written into the constitution instead.

He had already done the harder version of the same thing. In 1783, with the war won and the army unpaid and mutinous, officers at Newburgh contemplated marching on Congress; Washington talked them down, and the moment that reportedly did it was not the argument but him pausing to put on spectacles and remarking that he had grown grey and now nearly blind in the service of his country. He then resigned his commission and went home, which astonished Europe - George III is supposed to have said that if he really did it he would be the greatest man in the world.

The record is not clean and the same man held people in slavery for his whole adult life, over 300 at Mount Vernon by the end. He freed them in his will, alone among the slaveholding founders, and only on his wife's death - and the enslaved people he held were not his to free in the first place, many belonging to the Custis estate. He also had a set of dentures made partly from human teeth, some bought from his own slaves.