It is quite similar to PYX's background. Jasper, York and GGD were eating at Burger Khan one day, and Darktan sneaked into the kitchen and replaced York's burger with an X-Burger. When York and GGD picked up their food, York and Jasper dug into the X-Burger.
Jasper and York then started coughing severely, and they raced back to York's igloo where they coughed up their X-Antibodies. Jasper was blinded for a moment - and then he saw himself... but different. Xasper was green with glaring red eyes and black fangs. Jasper then knew that this was his X-Antibody, and that he was evil. Then, there was a battle between Jasper and York and PYX and Xasper. It was a tough battle, as York has a huge scar shaped like an X on her left flipper because of it, and Jasper has a bite mark scar on his right wing, but in the end York's ROFLCOPTER and PWN Missiles won. Xasper and PYX fled the scene before they would be captured by the CNIC.
Anger and hatred filled Xasper and PYX, and they wanted revenge. So they fled and joined Darktan's Army.