"Ali Baba and the Forty Thieves" is a famous tale from the collection known as One Thousand and One Nights. The story follows a poor woodcutter named Ali Baba who discovers a secret cave filled with treasure, hidden by a group of forty thieves. He learns the magical phrase "Open Sesame" to enter the cave and takes some gold for himself. When Ali Baba's brother, Cassim, learns of the treasure, he tries to take more but is caught by the thieves. The story unfolds with themes of greed, cleverness, and the consequences of one's actions, ultimately leading to a confrontation between Ali Baba and the thieves.