: So what is Aristotle's definition of a tragic hero?

Aristotle states in The Poetics that tragedy is a process of imitating an action which has serious implications, possesses magnitude and is enacted by persons who, through a corse of pity and fear, complete purifacation of the tragic acts.

A tragic hero is a person who has all the qualities to achieve heroic status, yet, through a tragic flaw/bad decision (dispute in translation), commits the tragic act/s and, because of these acts, is ultimately destroyed/ brought to a fall.

: But as I said, I don't see Melkor as really tragic, because, unlike for example Turin, Melkor chose to do evil.

Look at the definition above and then decide if it fits ;^)...I certainly think it does.