The Dark One is Morgoth and he's trying to get back through the doors of Night but lost his key.

I have a theory that the DO is not a physical being, but the spirit of pure evil.....in a simular way, The creator is the spirit of pure good. 

 

The DO is not just trying to escape, he is waiting for someone to act as his mortal vessle.  That is where the N'bleis

comes in....The DO will possess him, destroying his soul, and use his body to fight Rand.

He then has Logain or Alivia Balefire Rand, or does it to himself.

Which brings the Dark One back, and fulfills another prophecy. To live you must die.

and possibly the viewing of Min with Alivia helping him die.

 

I like this idea for one other prophecy....

Twice dawns the day when his blood is shed.

Once for mourning, once for birth.

Red on black, the Dragon’s blood stains the rock of Shayol Ghul.

In the Pit of Doom shall his blood free men from the Shadow.