Portraying Intelligent Undead in Tabletop Games

Why would GMs play unholy antagonists and Big Bad Evil Guys like morons?  In too many prepublished adventures, intelligent undead like liches, vampires, and ghasts are played as rash, unthinking, bumbling buffoons.  Jeremy presents alternate ways of thinking.  He gets into the mind of an ageless creature and hopefully gets your thoughts going on how to role play these rare, intelligent, monsters.