Cassim is the greedy older brother of Ali Baba in Ali Baba and the Forty Thieves. After Cassim's wife discovers Ali Baba's new wealth, Cassim bullies his brother into revealing his secret. He then enters the cave to take as much treasure as possible, but is so excited that he forgets the magic words to reopen the door and leave. The thieves find him and kill him. Ali Baba goes looking for him and finds his body quartered and hung at the entrance as a warning. He takes the body home and his slave girl Morgiana sets about making people believe that Cassim died naturally. She has a tailor, Baba Mustapha, whom she has secretly sew the body back together. However, the thieves later encounter Baba Mustapha, question him, and track Cassim's body to his home.
- In Aladdin and the King of Thieves (1996), the forty thieves appear, but Cassim is the name of their leader and Aladdin's father.