It's no accident that George Washington comes off a little wooden in history books. This Founding Father carefully positioned himself in life (mounting his white horse on the outskirts of towns in order to make a regal entrance) and in death (his wife destroyed all but three of their private letters) to be more monument than man. But Joseph J. Ellis splendidly dissects Washington's character and its impact on the not-so-in-evitable birth of a nation, weighing his ever-simmering ambition against his strict self-discipline. Ellis slips up when speculating about Washington's marriage, dismissing scurrilous historical rumors (ahem, ''George Washington slept here'') without providing specific evidence. But overall, His Excellency provides a fascinating study of the man and his times.