Stormtrotter is found by Princess Celestia and Luna with no memory. His identity is taken from him through his loss of who he is, and an X shaped scar where his cutie mark should be, leaving him purposeless and making him the object of stares and rumors. His story will unravel as time goes on, but things are probably going to be pretty dire for poor Stormtrotter.
He is a rather brooding and moody pony. Because of his cutie mark being removed by unknown forces, he spends time flying on his own and staying awake during the night to watch the stars and the moon. He feels bitterness towards all other ponies because of their cutie marks. In a way, he is like a filly, lost and trying to figure out who he is, only without any hope of regaining his cutiemark.