The "Forty Thieves" is a famous tale from the collection known as One Thousand and One Nights, also called Arabian Nights. The story follows Ali Baba, a poor woodcutter who discovers a secret cave filled with treasure, guarded by a group of forty thieves. The thieves use the magical phrase "Open Sesame" to enter the cave. In the tale, Ali Baba's cleverness and resourcefulness help him outsmart the thieves. His brother, Cassim, is less fortunate and meets a tragic end due to his greed. The story explores themes of wealth, cunning, and the consequences of greed, making it a timeless classic.