In life Derrick was a terribly rude and condescending king, however he was a mostly just warrior king as his time demanded of him but often put his foot in his mouth. He ended up offending a witch who cursed him to live and undying life to serve his kingdom. At first he believed the curse a boon, an undying life to protect and serve his kingdom, but as with all things time took its toll. His kingdom fell into obscurity, his people in the time of peace and prosperity forgot the blood the warrior king shed so that they could lead a life of peace.
A curse is still a curse, and eventually Derrick longed for the peace of an eternal slumber. However the only way for him to life the curse was to treat his people as his equal, and for a proud man long lived or un-lived he still had a lot to learn.