Tragedy, in the classical sense of the word, is defined by Aristotle as “a representation of an action… and by exciting pity or fear it gives a healthy relief to such emotions”. Every tragedy needs a tragic hero, and in Othello, we have just such a man, one who fulfills every requirement of the genre: “a man not pre-eminently virtuous and just, whose misfortune… is brought upon him not by vice… but by some error of judgement.”
Shakespeare’s Othello is a Moor, and he falls in love with the beautiful and virtuous (two qualities that often went hand in hand in Shakespeare’s writing) Desdemona, the daughter of a Venetian nobleman. On hearing of her supposed infidelity with the noble Cassio, Othello’s jealousy gets the better of him, and, fuelled by the poisonous Iago, Othello vows to take vengeance on his utterly innocent wife.
In his soliloquy in Act 5, Othello is cursing the stars for their intervention in his life. Although seemingly maddened by jealousy and rage, he vows not to mark or blemish Desdemona in any way. As Othello is torn apart by grief, his lament is made even more pathetic by the quite beautiful image of ‘monumental alabaster’, a type of porcelain used for making ornaments, famed for its whiteness and smoothness. This image of perfection and eternal beauty is one last poignant reminder to the audience that Desdemona is quite innocent of any offence, yet it also serves as a devastating indication that her end is nigh.
Eventually, Iago’s plotting and scheming is made clear to Othello, but only after he smothers Desdemona in their marital bed. The heartache and anguish that follows as Othello realises how he has been played and made to look foolish, is almost tangible, and his own end is as inevitable as his love’s had been.
He gathers himself one last time, regaining some of the dignity and eloquence for which he was so respected at the beginning of the play, to offer one last plea.
The tragic hero must always prepare to meet his end by coming to terms with his flaws and acknowledging his failings. The audience’s resulting pity is part of the emotional purification that this self realization brings about, but it is also followed by the hero’s death.
Here, Othello’s pride means that he will not allow anyone else to take on that responsibility, and he stabs himself as he kneels by Desdemona’s body. But his last few lines are amongst some of the most hauntingly moving lines that Shakespeare ever penned. The imagery of loss, love and lamentation that follow each other in quick succession suggest that far from losing his mind or falling prey to the ‘green-eyed monster’, Othello actually suffered nothing more than to fall hopelessly and utterly in love, in a way that left him completely powerless to control his emotions or his desire for vengeance.
So; a mighty soldier, a respected leader, and a proud man – one with every worldly advantage – is humbled and driven to destruction by the one thing he had no control over; his love for a woman. That's the pity...
Why Shakespeare creates sympathy for Othello is a mix of human and dramatic reasons; we care more about people's suffering if we are given a chance to know them, and if we sympathize with them and/or think well of them. The sympathy makes the later suffering more important.
As to how he creates sympathy, well, that's much of the play. Early on we see people (Iago and Roderigo) plotting against Othello; this makes me want to be on his side before I even see him. They stir up racial prejudice against him, and this makes me sympathetic to him; I then like him more when he stays cool in the face of it and calmly explains how he charmed Desdemona. After that, the main ways this is done is through showing Iago's evil plans and Othello as vulnerable to them.