Sephiroth.
Once he'd been a hero. Parents would tell their children stories of him, as if he were a legend larger than life. He was a General who commanded not only SOLDIER, but could also take command of the Shinra Army when it was deemed fit. People wanted to be like him, people joined Shinra just for the slim chance of meeting him.
But then things changed. First his friend and fellow First Class Genesis defected, and then his other friend and fellow Angeal followed. To the outside world Sephiroth seemed cold to it and even within Shinra he was seen as a spoiled brat, but inside the stoic man was breaking. The invisible cracks were revealed only years later when he was sent to Nibelheim with Zack Fair and a few Infantrymen to investigate a reactor malfunction. The orders themselves seemed strange. Why send a SOLDIER to do a technicians work, let alone two? The truth was known only to President Shinra, for Professor Hojo had formulated those orders. His grand experiment was to be given a great test and the insane but brilliant man wanted to see what would happen after Sephiroth would see the name of the woman he believed was his mother imprinted at the top of the reactor stairs.
But Hojo had only intended for that one factor and could not have planned for the reappearance of Genesis, who had been presumed dead years before at the hands of the aforementioned Zack. Words of poison were spoken to Sephiroth on that night, words that burrowed deep within his troubled mind and drove him into an obsessed frenzy. The basement library of Shinra manor became his home. He barely slept, he didn't eat and he read and read. And then the cracks crumbled and the foundation of his sanity collapsed. Believing Jenova was an Ancient who had been betrayed by humanity, he swore his revenge and burned Nibelheim to the ground, killing whoever crossed his path and bathing his sword, Masamune with their blood.
The efforts of Zack Fair and the Infantryman Cloud Strife put Sephiroth down for that act, only for Sephiroth to return four years later and continue his revenge against the planet he felt had betrayed him and his mother. Sephiroth was no longer a hero, but the greatest of villains. Rather than speaking of him with awe and reverence, parents now used him as a horror story. He was the newest boogyman. You'd best behave or Sephiroth would get you.
But Sephiroth was no villian, and he did not truly deserve the hate thrown at him. He had not chosen his insanity, he was a product of his environment and upbringing. Raised within the walls of Shinra, given nothing but the barest essentials and given no chance to be a normal child, Sephiroth was doomed from the start. Indeed, he did not have any friends until Angeal and Genesis. Friends he was allowed to have as they were fellow experiments made by a presumed inferior scientist and Hojo found it amusing that they would interact. He longed for the warmth of a mother he had never known, imagined wonderful things about her, never knowing that his real mother had been but a human woman named Lucrecia Crescent. If he had felt true kindness, would he have become the feared monster? If he had been raised as a boy ought, would he have snapped when his world was thrown upon its head? Could he in death be redeemed by even just one heart knowing of his sins and saying 'I forgive you'? Questions that cannot be answered, for his soul wanders alone and unloved and no one can possibly reach it for the hatred it wears as its shroud.