Describe Sonny's personality and why he acts the way he does."Sonny's Blues" by James Baldwin

In the exposition of Baldwin's "Sonny's Blues" Sonny is
the stereotypical resident of Harlem:  the drug-addicted loser.  He is on the outside of
society, and shows little potential to assimilate into mainstream America.  While he
seems to be the antithesis of his narrator brother, Sonny and his brother both come from
the "killing streets"; the author remarks upon another similarity as they take the cab
ride through Harlem,

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...it came to me that what we both were seeking
through our separate cab windows was that part of ourselves which had been left behind. 
It's always at the hour of trouble and confrontation that the missing member
aches.

Sonny is not
talkative.  As the brother and his family and Sonny dine, the narrator recalls that
Sonny and the father fought because the father was frightened for Sonny.  But, it does
no good to fight with Sonny; he "just moves back, inside himself."  There he cannot be
reached in his privacy, but the brother knows that Sonny is vulnerable.  For, Sonny
suffers greatly.  His solace has been his music.  When Sonny comments that the street
singer must have suffered greatly to be able to sing as she does, he indicates that he,
too, that he has endured much to arrive where he is when he plays at the
nightclub.

"I sensed myself in the presence of something"
the narrator writes about Sonny on the day of the funeral of his mother.  He knows that
Sonny has talent, but is vulnerable to the problems of life. Still, for Sonny music is a
medium in which he can live and breathe although it is an atmosphere which is not like
the narrator's.  Instead, Sonny is "loose and dreamlike all the time."  But, while his
music has been an excuse for the life he has led, it becomes, at the end of the story,
the salvation of his soul.  And the music touches the narrator, too. "My trouble made
his real."  As he sits in the nightclub, the narrator realizes that the music has helped
Sonny remain free as he has an outlet for his suffering, just as it is an aid to
everyone to be true to what they are.