Long before time had a name, there was the Realm of the Oni and the Dragon.
The first. The Dragon had the power to create. The Oni had the power to destroy. Their war was never ending. But a child arrived, born of both worlds. The child understood the power of both. Without one, you could not have the other. But when the Oni and the Dragon fought over which side the child should choose, the child abandoned their world to start a new one called Ninjago.
After the First Spinjitzu Master created Ninjago, he fathered two sons of his own. He thought he could escape the war. He saw the evil of the Oni was waiting to be unleashed in one of his sons, Lord Garmadon! It was up to Master Wu to control his brother's undying thirst to destroy.