Napoleon was very untrustworthy because he broke all of the commandments for example, "No animal is to sleep in a bed" when in the book Napoleon and the rest of the pigs were all sleeping in beds. Also Napoleon was very arrogant. He made a song about himself called "Comrade Napoleon" , which was mostly about how great of a leader he was, even though its not true.
In this story, the theme "Power Corrupts" relates to the story because of how Napoleons "fame" got to his head. Even though he was just another pig, he made himself feel as though he was above every other animal on the farm. Making the other animals call him leader, and by him breaking all seven commandments he thought as thou he was superior to the farm. Napoleon was very big-headed and controlling.