Every single writing tip I've found on Pinterest says that starting a story with backstory is boring. Too bad, you get it anyways.
Many years ago, the country of Dreamland was at peace, ruled by a wise king and queen. Dreamland was full of many riches and resources, but most importantly, it held the legendary Fountain of Dreams.
The fountain created the dreams of all the world's citizens. Only a select few were allowed to see it, as it needed to be protected. One touch from a user of dark magic would taint the fountain forever, causing endless nightmares and despair.
One unfortunate day, this came true.
A malevolent sorcerer named Dark Mind watched the kingdom from afar, eager to get his hands on the riches that lay within the land. He and his two powerful sons, Nightmare and Zero, attacked Dreamland with their army of demons. Dreamland had no means of defending itself, and quickly succumbed to the attack. The king and queen were executed, and Dark Mind took their place.
Nightmare, however, had ulterior motives. He knew about the Fountain of Dreams, and quickly went to corrupt it. One dip of his finger, and the water turned black. Satisfied, he went to go celebrate with his family.
The next morning, when he woke up, he felt a surge of power in his veins. His father and brother were still weakened by the battle they had waged the day prior, and Nightmare saw a chance.
He mercilessly killed them both.
From that day forward, Nightmare reigned as King of Dreamland. As long as the people suffered from his curse on the fountain, he never aged, and retained his near godly powers. Generations passed, and the people lost hope of ever dreaming peacefully again.
Fate, however, knew that they would.