We'll bet that when you picked up Charlie and the Chocolate Factory, the last thing you were expecting to read about was spies. But spies there are. And ruthless ones, at that. Mr. Fickelgruber, Mr. Prodnose, and Mr. Slugworth are all chocolate makers who, we learn in Chapter 4, sent spies to Mr. Wonka's factory to steal his recipes.
Why would they do such a terrible thing? Grandpa Joe tells us that it's because they "had begun to grow jealous of the wonderful sweets that Mr. Wonka was making" (4.6). Unfortunately, this meant that Mr. Wonka had to shut down his factory for a time, until he hired the Oompa-Loompas, who could keep his secrets.
These chocolate makers are briefly mentioned again in Chapter 19, when Mr. Wonka tells everyone, "Old Fickelgruber would give his front teeth to be allowed inside just for three minutes! So would Prodnose and Slugworth and all the other rotten chocolate makers!" (19.3).
The one good thing about these greedy troublemakers is that they make Mr. Wonka seem even more amazing. He's the only one in the world who can make such delicious sweets, which means he's one-of-a-kind. There's simply no one else in the world who can make chocolate quite as well as Willy Wonka can.