Disclaimer: No, no, no; I don't own Harry Potter. Now release me.
The transfiguration professor of Hogwarts worked confidently into the Room of Requirement. This Room was simply a genius of the Founders, and provided an opportunity to perform dangerous experiments without anyone being the wiser. It was now looking like a...what did the muggles call it? Yes, a laboratory.
He had been working on this project for a long time. He was a genius in transfiguration, and an extremely skilled alchemist. From his research, he had stumbled upon the idea that as opposites exist in every part of the Universe, they also exist within the very soul of human body and soul. He had a morbid curiosity to know what would happen if somehow the suppressed and negative tendencies of human beings could be brought into the forefront, or better yet, ejected from the body? The world could then be made into a utopia, with good prevailing everywhere. The rejected parts can be killed off, or used for better animation of transfigured objects. Oh, the possibilities.
It had been hard work. Working to convert your soul to manipulate it with magic was too tough, as magic flowed from the core of soul itself. It was impossible for anyone to have enough power, as the divided soul takes away parts of his magical energy as well; think of it as trying to split up a pure energy, with the energy dissipating due to splitting before anything is achieved. He had used rituals, arithmantic calculations and even resorted to using the elixir of life when he was too injured to continue. But today was the day. He had in his hand a potion made by his friend Professor Horace Slughorn, which was ordinarily used to recognise one's inner animal for animagus transformation, but with the modifications, he hoped, would do his job. With a deep, calming breath, he consumed the potion, and a blinding beam of light filled the area. He, however, succumbed to unconsciousness.
-oOo-
Albus Dumbledore woke up with a groan. A nasally voice greeted him, "Ah, well. It seems that you're awake after all."
He stared in horror at the snake-like man in front of him. Normally, the defeater of Grindelwald would cower at the sight of no wizards, but something about this man screamed "Wrong" in his mind. He stood up warily and asked, "Who are you?"
"The world shall know me soon by a different name, and tremble in front of my might. But for now...you can call me your dark side. I am every desire that you kept suppressed, Albus," he grinned eerily, "Power is a great lust, no?"
"What are you saying?"
"Oh, grow up, Albus. This world is a stagnant place. It needs change, and someone strong must rule over them. The stronger must rule and not fuse with the weaker. I will soon wage a war against this world that shall shake it to its roots. The purebloods will join me, and we will cleanse our world of the taint of mudbloods, squibs and pathetic wizards."
"You're wrong!" He all but screamed, "You can't be me. These...These ideas never entered my mind."
"You can't lie to yourself, Albus. Remember your early days, how you never mixed with other children because you believed you were superior. No mudblood in school got help from you. Did you ever try to stop Griendenwald when he influenced that muggle from to Germany to wage the war which almost destroyed the muggles? The prejudice was always there, Albus, believe it or not. Guess you're finding my ideas too horrific as you're now your goody-goody self." He shrugged.
"You'll never find any support. No pureblood will support a wizard who has no birth name."
"Oh yes. Do you know, Albus, how wonderful the magic of this room is? I now know about the birth of a wizard named Tom Marvolo Riddle, his abilities, skills and political friends he'd made in his life. It won't be too sad if he suddenly dies now, and his body is occupied by another soul. Funny fact is that he seems to have had the same ideas in life; it won't be too suspicious. With your abilities, Albus, it will be child's play." His eyes were red with the gleam of the fanatic. "Well, here's your offer; Will you join me?"
In response, he sprung up and turned his wand on this wizard. He was going to destroy him before he could do any damage...ungggh.
He looked down at the fallen form of Albus with contempt. "Pathetic!" He spat. "I expected more from myself. Truly, compassion has made you weak, my other half." With a flurry of his robes, the terror was outside, and was soon to be known to the world as Lord Voldemort. The world feared him, and not one wizard cold stop him till the arrival of Harry Potter.
-oOo-
There were many questions in the minds of the fighters of light during the War. Why was Dumbledore so focussed on redemption? Why did he wanted to see the good in everyone?
They never knew that it was an earnest hope of his to rejoin his souls. He wanted to experiment on them to rejoin his other half...but couldn't. His inherent goodness stopped him, and made him see only the good in everyone.
But why did he change later in his life, then?
Lord Voldemort had created Horcruxes; soul anchors, if you will. When he died, he wasn't truly dead and his life was tethered to them. None of them knew, however, that the spell had a shelf life; it expired just after his defeat...
He was too far away and too insubstantial to regain his soul or merge with his counterpart; he remained as he was, his body and mind unaffected. The soul anchors, too, didn't release their hold, but the echoes of emotions, memories and ideas flowed; the acts of necromancy, voodoo and dark rituals invaded a mind which had slept without occlumency barriers in years...
Albus Dumbledore woke up with an identical maniacal grin his face, the one he had dreaded years ago. The goodness in him was trampled by his lust for power, as he felt power flood his core. The elder wand seemed eager to serve its new master. In the empty room, he whispered, "Harry Potter; think you can take away the glory of defeating Lord Voldemort from me? That isn't going to happen." Instructions went away to Hagrid and Minerva; they had work to do.
As he looked at the mirror, he found his eyes flashing red. With an effort, they changed to give him a twinkling effect, about which many students, and Harry Potter would wonder later.
The end...or is it?
A/N: Just a little fun at the plot of Robert Louis Stevenson's amazing story, "Dr. Jekyll and Mr. Hyde." Read it if you haven't already; it's a classic. Thanks for reading and please review. Reviews make me happier, and happier me means better quality work.