The "Dummies" Author is the character who wrote the famous "For Dummies" books.
Whilst Bart is looking at the Books for Dummies section at the Festival of Books in Springfield he started reading Moby Dick for Dummies, he asks the author how he writes all these books. He replies by saying he doesn't know then walks to the bank with a money bag.
Bart says to the the author that his hat's a bank so he starts to empty potato chips from the hat. Bart looks confused about the potato chips but the author tells him he's now rich.