Simplify the following text for a Grade 11 native English-speaking person.
Original: Casaubon , who believed in the reality of spirits , argued in his introduction that Dee was acting as the unwitting tool of evil spirits when he believed he was communicating with angels . This book is largely responsible for the image , prevalent for the following two and a half centuries , of Dee as a dupe and deluded fanatic .
Simplified: Because Casaubon wrote in his introduction that Dee was really dealing with evil spirits when he believed he was communicating with angels , Dee was thought of as deluded for some time .