Shame
You have everybody fooled.
You beam and wink, looking handsome for the camera that flares brightly and belches bursts of purple smoke. You laugh and chat, knowing without a shred of doubt that you are safe, here in the security of influence, fame, and fortune.
Sometimes—when you sit in the dark, staring at faintly glowing embers, wallowing in the atrocious armchair your father gave you for your twelfth birthday—you wonder what people would say if they knew who you really are.
No, you correct yourself every time you think that, if they knew who you really were.
Either way, you don't think you could stand the shame.
Because that's all Albert Diefendorf ever was—a shame.
Your years at Hogwarts were the worst of your life. You spent seven years in that castle, enduring taunts and pranks, striving to achieve, so that maybe, maybe, the teasing and tricking would stop.
When you had first sat in front of the whole school, the Sorting Hat over your eyes, past your nose, right down to your chin, it had hummed and twittered in thought, and you had been so proud because you thought that meant you had all the traits and it couldn't decide which you had more of. By the end of your second year, you realized: The Sorting Hat couldn't decide because you had none of the traits. You weren't quite brave enough for Gryffindor, or smart enough for Ravenclaw, or loyal enough for Hufflepuff, or cunning enough for Slytherin.
In the end, you were The Ravenclaw-Who-Failed. You didn't measure up. They laughed at you.
Your short brown hair had always been a rat's nest from climbing trees and sleeping in odd places. You were a mess. They kicked your sleeping body curled up behind the statue of Boris the Bewildered.
You were short for your age, only five-foot-three in fifth year. They called you a shrimp. You didn't pose any threat; you were an easy target. Even a group of pranksters four years your junior—James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew—dared to play humiliating tricks on you.
But there wasn't anything you could do about it. Your grandparents had left Germany and their influential rank in the German Wizarding World during the Dark Lord Grindelwald's rise to power. No one at Hogwarts cared that your great-grandfather had served directly under the German Minister of Magic, or that he had only barely lost to Allard Dodd in the 1910 election. You couldn't even brag that your parents were Unspeakables high in the mysterious hierarchy of the Department of Mysteries or that they were invaluable members of the Order of the Phoenix—the largest and most successful resistant group since He-Who-Must-Not-Be-Named started to grow power in 1957—because that was top secret information.
You were just the strange, dumb Ravenclaw with a lisp and a light accent from the years you spoke German at home.
You hated it, especially the fact that you had no friends. You don't think anyone, besides, perhaps, the Headmaster, knew that you had found your father's dead body on the porch on your thirteenth birthday. Or that your mother had gone missing half-way through your sixth year and turned up at your aunt's house eight months later, dead, cut up into small, two-inch by two-inch pieces and dumped in a Muggle oil drum.
So, instead of curling up in a long forgotten house on the other side of the world like you wanted to, you went about killing Albert Diefendorf.
You changed your name, your hair, your eyes. You fixed your teeth, your nose, your skin.
You made yourself perfect.
Then, you made yourself a life. You spent a whole year carefully creating and memorizing every last detail of this fake life you composed. You pored over calendars and books, getting dates straight and choosing details for an exciting life. You scoured little known Eastern European newspapers and magazines for adventures to "take".
Finally, you gave the ball a giant push and it rolled.
That's why you're here—beaming, winking, laughing, chatting, flirting as you sign book after book of your supposed autobiography and extended versions of your long, perilous escapades.
No one would ever think that the brave and clever Gilderoy Lockhart had once been the clumsy and awkward Albert Diefendorf.