When he was a baby, Xavior has an unnamed father that took care of him after his mother died. When he was 3, he met Baby Bowser in the park with Yoshi. He and Baby Bowser "socialized" with each other while Xavior's unnamed dad and Yoshi talked to each other. A few years later, an unnamed sister was born. Xavior hated her because she always messed things up. While he was sleeping, he dreamed to be an evil villain, rule the world and kidnap princesses. One day, he went to Bowser's house and he had the same dream. Many, many years later, the Mushroom Kingdom was born. He and Bowser picked which place they should rule first, and they picked the Mushroom Kingdom. They planned what they should do, and they started kidnapping Princess Peach. Mario always saved the day. They tried many more times, and Xavior though that they should take a break. Bowser called him a quitter, and he said he'll never give up, and if Xavior doesn't want to battle evil, he should just go home. Xavior didn't reply, but he went back to his house, and he took a nap. A few years later, he and Bowser forgave each other and worked together to rule the Mushroom Kingdom. Bowser called Xavior his best friend, and he appreciated it.
Taking Over Bowser
Xavior Koopa took over Bowser's place as the final boss in New Super Mario Bros.: Clash of the Koopas. After Mario defeats Bowser in World 18, Mario unlocks the cage Princess Peach is trapped in. She floated to the ground, and all of a sudden, Xavior comes from the ceiling, and he brings Peach a few feet away from him and Mario. He tells him that he couldn't wait anymore, so he took over his place. When Mario defeated him, his face was red and he screams loudly. He says that he'll get his revenge one day and that Mario can have Peach for now.