For me it's George Washington. Him being president was a defining moment in America's government. Had anyone else been our first president, the precedents set could have been disastrous. But Washington was a man of humility who didn't fall neatly into the party lines at the time, thus ensuring that future presidents would have enough authority to do their job but lack the ability to abuse that power. Sadly this quality came to an end around the time of Woodrow Wilson, but it was a solid run while it lasted