After completing Long Live The Queen, Dungeons and Devils, and Spoils of War, the game unlocks two additional campaigns. You can either help Queen Catherine fight back the invaders and liberate Erathia or you can join the forces of darkness and build an army of the undead. For this playthrough, I'm going to help the necromancers first.
With most of Antagarich embroiled in chaos and corpses piling up by the thousands, the necromancers of Deyja sense the perfect opportunity to invade.
The first thing they do is raise King Gryphonheart, former ruler of Erathia, from the dead. To me, this seems like an incredibly stupid idea. King Gryphonheart was the necromancers' enemy and would undoubtedly be furious at being reanimated. Did they need a general that badly?
Maybe that's the point. The necromancers didn't think before acting. At this point in the timeline, Finneas Vilmar is the one calling the shots in Deyja. In one of the later storylines, we learn that Finneas is essentially a puppet who is placed on the throne by Sandro the lich as part of the latter's plan for world domination. In short, Finneas is a useless idiot who's in over his head.
Finneas was too stupid to have one of his underlings conduct the ritual. It's completely fitting that the undead King Gryphonheart's first order of business is to choke him to death and take the throne.