Tragic heros have to have these things if they are to be considered a tragic hero:
1. Usually of noble birth
2. Hamartia – a.k.a. the tragic flaw that eventually leads to his downfall.
3. Peripeteia – a reversal of fortune brought about by the hero’s tragic flaw
4. His actions result in an increase of self- awareness and self-knowledge
5. The audience must feel pity and fear for this character.
Therefore Othello's nobilty and dignity lies in his profession as a soldier, and his background as a moorish prince. This creates a feeling of descent in the novel and he is brought down from being "valiant" to Iago's base level, and creates the downfall that is nescessary to tragedy.