Power vs. Responsibility genre in Film: Where do we stand?

I was compelled to take a stab at this topic, based mainly on the previous discussions in the X Men, First Class post; also, to a less degree, from all the critical decision-making while playing SWTOR game (yeah, the game is that detailed). 

It’s a bit contrived so bear with me.

Fallen Heros: The blurred grey line between them and the Anti-hero

Well, now that we have a good discussion in regards to the hero/anti-hero archetype, I’m curious to see if we can take this topic a bit further, and slightly darker, so to speak. Since we can agree on anti-hero types as complex characters, how would be describe a character that possessed true heroic ideals, but due to some sort of tragedy (which could be anything) slowly and inevitably become the full antagonist he/she once strived so hard to fight against. In short I present the Fallen hero.