In the book, Arthur Slugworth is one of Willy Wonka's rival chocolatiers. Slugworth, along with Wonka's other rivals Mr. Fickelgruber and Mr. Prodnose, sent in spies to steal the secret recipes to Wonka's treats for them.
Having obtained these, he began making candy balloons that a consumer blows up to incredible sizes, and then causes to burst before eating them; a plagiarized invention.
The work of Slugworth (along with the other rivals) came close to ruining Wonka's factory. Wonka was forced to close his factory and fire all of his workers. A few years later, Wonka's factory began working again (operated exclusively by Oompa-Loompas) and his work continued to dominate the candy industry, with no rival able to plagiarize his work because using the Oompa Loompa as his workers enables Wonka to operate his factory without regular employees and keeping it off-limits to the public, so none of the spies can infiltrate.
Slugworth is never heard from again, but it is stated that Slugworth, Prodnose, or Fickelgruber would each give their front teeth to enter Wonka's inventing room (a laboratory) for 5 minutes. It's presumed that Slugworth, alongside Prodnose and Fickelgruber, may have continued their businesses, but as Willy Wonka stopped hiring human employees, it's likely they no longer were able to produce special treats like those of Wonka.
In the 1971 film Willy Wonka and the Chocolate Factory, Slugworth's company is in business. Inside Bill's Candy Shop, Wonka's products and signs are the most visible; but Slugworth's Sizzlers are also prominently displayed, and one is even sold to a child called June Marie.
Things that are also seen are signs for Fickelgruber's candy. Grandpa Joe describes Slugworth as the worst of Wonka's rivals, telling Charlie that he was one of those who sent his spies in dressed as Wonka workers to steal Wonka's Recipes.
A man calling himself Slugworth is a prominent character later in the film-where he was portrayed by the late Günter Meisner. As each Golden Ticket is found, he approaches the finder and whispers something into his or her ear. After Charlie finds the last ticket, the same man then approaches Charlie as well, and delivers what is presumably the same speech he has given the other children.
He introduces himself as Arthur Slugworth, president of Slugworth Chocolates Incorporated, and bribes the child to bring one piece of the newly invented Everlasting Gobstopper to him so that he can discover and plagiarize the formula. Two of the children respond to Slugworth's bribe. Veruca Salt crosses her fingers behind her back when Willy Wonka asks the children to promise not to show the Everlasting Gobstopper to anyone else.
Mike Teevee asks his mother what secrets they can sell to Slugworth; his mother is also heard telling her son to keep his eyes peeled and his mouth shut. Grandpa Joe also responds near the end of the movie. After Willy Wonka snaps at him and Charlie Bucket for violating the rules by stealing Fizzy Lifting Drinks and bouncing up the ceiling which needs to be washed as a reason of why Charlie didn't get the prize, Joe threatens to give Slugworth the Gobstopper. However, Charlie can't bring himself to betray Wonka and thus returns the Gobstopper to Wonka.
Touched by this display of selflessness, Wonka forgives the theft of the Fizzy Lifting Drinks and reveals that the man isn't actually Slugworth, but a non-Oompa Loompa Wonka worker named Mr. Wilkinson, and that his "offer" was a morality test, which only Charlie passesd.
The movie doesn't explain how the false Wilkinson was able to approach each winner so soon after they found their tickets. However, it's implied that Wonka somehow managed to keep track of each ticket's destination and then he told Wilkinson where they are most likely to be found.
Slugworth only makes a split-second appearance in Tim Burton's Charlie and the Chocolate Factory where he was portrayed by Philip Philmar. He receives a secret recipe from fellow envious candymaker Prodnose and both of them were not heard of again.
Tom and Jerry: Willy Wonka and the Chocolate Factory
In the film, he invades Wonka's chocolate factory to steal a special candy known as the Everlasting Gobstopper. Despite his seemingly antagonistic nature, his reveal as being an employee of Wonka like the original 1971 film is revealed. He was voiced by Mick Wingert.