For over 1000 years Klaus has been trying to a break a curse that bound him to a moonstone. He created the myth of the sun and moon curse in order to help find the moonstone and the Petrova doppelgänger that was needed to break the actual curse. His goal was to bring out his werewolf side so he could sire his own super race.

In 1492, he finally got his chance to break his curse when he met Katerina Petrova, the final piece for the ritual. He kept her entertained until the full moon, but was unaware that she found out what he was and what he wanted from her, causing the Katherine to escape from him. After Katerina turned into a vampire he assumed that her family line ended with her and that his chance to break his curse was forever gone, Klaus traveled to Bulgaria and slaughtered her entire family for revenge.