The Devil's Eye is the world's biggest diamond and the main reason of Madame Medusa's ambition. It is the main plot element in Disney's The Rescuers.
The greedy Madame Medusa would do whatever it takes to get her hands on the diamond. It used to belong to pirates that buried their treasure in a cavern in the Devil's Bayou.
After the explosive showdown at Madame Medusa's riverboat destroyed by fireworks in the Devil's Bayou that ended with the young orphan Penny with her recovered teddy bear (with the diamond placed in it) rescued by both Bernard and Miss Bianca, Mr. Snoops got away alive laughing, and Madame Medusa at the mercy of her 2 angry pet crocodiles Brutus and Nero, the Devil's Eye is donated to the Smithsonian Institute.