In this book, the leader myth and personality cult are, of course, built up around Napoleon. The "person" who does most of the work of creating this cult and myth is Squealer.
Over the course of the book, the animals are encouraged to think of Napoleon as a perfect leader. They are told that without Napoleon, they would surely go back to being abused by the humans.
Another example of how this cult is built up is when they stop referring to Napoleon by his name. Instead, they start to use titles to refer to him -- titles that emphasize how much they need him.