So, we all know the main character is the Dovahkiin, but how will you find out? Let's post our own theories about this, get some hype and kill time until E3.
Mine:
We all know how the game is going to start, you are facing your death, so when the executioner is going to chop your head off, a Dragon comes out of nowhere, people start to panic and start running, since you're with chains and everything execution related, it's impossible for you to run, so the Dragon thinks you're an easy prey, he comes in for the kill, your character starts to shout in panic, and with a little bit of luck, you scream something in the dragon tongue (maybe Fus?) the Dragon takes the impact and flies away. Esbern is amongst the panicking crowd and he notices what you did, so he approaches you and well, the adventure begins.
What's your theory about this?.
RuGaard snarled at the guard in front of him, who turned around with a sinister smirk and raised his arm, striking RuGaard across the face, to RuGaards sincere pleasure, the guard's smirk twisted into a grimace as his unarmoured hand struck the argonians hard scales, RuGaard, however, barely felt a thing. The guard turned forward again, trying to act triumphant, but failing miserably, as the whole patrol had saw the failed blow, a few of them let out muffled snickers and a distorted snort that led to more snickering and the guard who had attempted to hurt him, tried his best to hide his face from the others. Atlast they entered the arena, RuGaard flinched as the light stabbed at his eyes like daggers, and the shadows around them receeded, the guards blinked a bit, but they hardly seemed effected by the tremulous sunlight cascading over the arena walls. A mighty cheer broke the silence, and RuGaards eardrums. RuGaard let the guards guid him, he felt wood against his neck, and trembled slightly, after a minuite longer he regained his eyesight, though it was still a bit blurry. In front of him stood a Nord clad in black, a massive axe held by both hands. He raised it into the air, RuGaard couln't move his arms, the guards held him down onto a cold slab of stone, he shifted a bit, trying to get a better veiw of the massive Nord, then, a deafening roar slashed through the cheering, what was that? RuGaard couln't see anything! Of what he could see, smoke covered the horizon, guards were shouting for water and running out of the arena, then there was a scream, a terrible scream, that chilled RuGaard to the bone. The weight from the guards that held him down vanished and the executioner rushed behind him, there was a clash of metal, and another death scream. A shadow loomed over him, RuGaard's breath quickened as a hand fell to his shoulder and helped him off the stone slab, slashing through his bonds with a mighty sword. RuGaard turned around to see an old man, splattered with blood.
"Who are you?" RuGaard asked.
"I, am a Blade."
Well, my theory is that while a dragon attacks the town nearby Esbern comes to save you. Then you flee the town to learn what Esbern already knows, you are Dragonborn.