Tragedy is defined as...
...a serious play in which the chief figures, by some peculiarity of character, pass through a series of misfortunes leading to the final catastrophe.
In light of these definitions, the character in August Wilson's Fences that seems to be truly tragic is Troy Maxson. By comparison, Rose has her faith and a sense of love that keeps her from becoming tragic. She is able to put her own feelings aside to care for Troy's love child when his mistress dies in childbirth. And even at Troy's death, she defends his actions during life...
...he meant to do more good than he meant to do harm.
Gabriel, Troy's brother, might seem tragic at first because of his physical handicap. The head wound he received during the war has left him believing that he is God's Archangel, Gabriel...
...a messenger to humans from God.
However, his life is very simple. He sees things that others throw away (the discarded fruit he tries to sell and the broken trumpet he tries to use to open heaven's gates for Troy at the end) as worthy and special. Perhaps this is why he so loves Troy: the man who was abused by his father and has served a jail sentence for robbery and murder. Troy is bitter about things that have happened in his life, but Gabriel loves him all the same. Ironically, Troy has used money Gabriel received because of his injury to buy his house and pay Gabriel's "rent." Even with this shady dealing—if Gabriel could ever be aware of it—it is doubtful that Gabriel would begrudge his brother the money. Gabriel is not tragic, but his spirit is uplifted.
Cory loses his chance to play college football because of Troy's skewed view of the world and the new day and age his son lives in. Troy throws Cory out after a series of arguments first about football, and later in the face of Cory's criticism in Troy's taking Gabriel's money. However, Cory is given a choice at the end. He has already joined the Marines, and is preparing to take a new job and marry. These are things he has made work for him that his father could not. When it seems he will not attend his father's funeral because of the anger between them, Rose (his mother) tells him that not attending the funeral will not make him a man. Cory chooses to go and pay his respects even though his father dealt harshly with him in life.
Troy, then, is the most tragic figure because for him, he can never put the past behind him. He is locked in a destructive cycle that his father began. The violence visited upon him, he turned on another and landed in jail. When he was released the major league ball teams were integrating baseball, but Troy (with a great deal of promise) was too old. He is bitter for this, and even passes that on to Cory when his chance comes with a college recruiter. Rose reminds him:
You can't visit the sins of the father upon the child.
But Troy has done just this with Cory, by way of his father's parenting with him. Troy has a loving wife, but he notes that because responsibilities weigh too heavily on him, he becomes involved with Alberta and his marriage crumbles.
When Troy dies, Rose reveals an irony to Cory:
Your daddy wanted you to be everything he wasn't...and at the same time he tried to make you into everything he was.
Tragically, Troy could not manage his life or help others.