Initially she presents Boo as someone to fear. He presents him through stories and myth. Scout thinks he is
".... six-and-a-half feet tall, judging from his tracks; he dined on raw squirrels and any cats he could catch, that's why his hands were bloodstained....... There was a long jagged scar that ran across his face; what teeth he had were yellow and rotten; his eyes popped, and he drooled most of the time." (pg 13)
When the children asked Atticus about him, Atticus would just say to mind their own business and leave him alone. So they had to get their information from Miss Stephanie Crawford. Supposedly, according to Ms. Crawford, Boo had been cutting articles from The Maycomb Tribune. When his father walked by him, he stuck his scissors into his father's leg. Then he went back to cutting out his articles. Boo was thirty-three years old then. Boo is presented a having mental problems and kept at home because they didn't want to jail him with the Negroes and the basement of the jail was too damp.
He is kept a secret throughout the book, but the children receive little presents left in a tree trunk and it is INFERRED that they came from him.
At the end of the book, Boo kills Mr. Ewell when he attacks the children. The sheriff believes he was a hero for doing that but doesn't want to let the rest of the town to know because
"If it were any other man, it'd be different. But not this man, Mr. Finch" (pg 276)
At the end of the book, the reader sees Scout take Boo, or Arthur as he is really named, by the hand and lead him out to the porch.
"Feeling slightly unreal, I led him to the chair farthest from ATticus and Mr. Tate. I was in deep shadow. Boo would feel more comforatble in the dark." (pg 273).
At the end of the book, Boo has transformed from his horrible myth the children had imagined to a meek, quiet man who protected the children and saved their lives.