Bewigged, muscular and for his day unusually tall, adorned in soiled, rumpled clothes, beset by involuntary tics, opinionated, powered in his conversation by a prodigious memory and intellect, Samuel Johnson (1709-1784) was in his life a literary and social icon as no other age has produced. "Johnsonianissimus," as Boswell called him, became in the hands of his first biographers the rationalist epitome and sage of Enlightenment. These clichEs--though they contain elements of truth--distort the complexity of the public and private Johnson. Peter Martin portrays a Johnson wracked by...