Cassim is the father of Aladdin. Long before the events of the the first film, he left his wife and young son in order to find a better life for the poverty-stricken family. While he was gone, Aladdin's mother died, leaving Aladdin as a presumed orphan. At some point, he became involved with the Forty Thieves, eventually becoming their leader, and began a search for the Hand of Midas, which could turn things into gold.
Role in the film
In the film, Cassim leads a raid on Agrabah in an attempt to find the Oracle, which could answer a single question about any subject, in the hopes he could find the Hand of Midas. The raid is ultimately unsuccessful, but interrupts and ruins Aladdin and Jasmine's wedding.
After the wedding, Aladdin unexpectedly finds the Oracle, and learns of the survival of his father, whom he had presumed was deceased, and his location with the Forty Thieves. Aladdin tracks the Forty Thieves to their hideout, but learns that his father is actually Cassim, their leader, rather than a prisoner.
Aladdin gains entrance into the Forty Thieves by fighting and defeating Sa'Luk in a fight. After learning from Cassim the real reasons for his departure from their family, Aladdin decides to help Cassim get into the palace. However, Cassim is convinced by Iago to rob the royal treasury and is arrested. Aladdin helps Cassim escape prison, but refuses Cassim's pleas to flee the city.
Cassim returns to the Forty Thieves with Iago, where he discovers that Sa'Luk has ursuped control and turned the Thieves against him. Cassim is then imprisoned by the Thieves. In order to prove his loyalty to Sa'Luk and the gang, Cassim uses the stolen Oracle to locate the Hand of Midas and leads the Thieves to its location, a marble fortress on the back of a gigantic sea turtle.
Aladdin eventually returns, having been warned by Iago of his father's capture, and releases him. The two reconcile and recover the Hand of Midas. Cassim and Aladdin, in an attempt to escape the now submerging fortress, throw the Hand to Sa'Luk. Unaware of the legends, Sa'Luk grasps the Hand by its golden hand rather than the wooden handle, and is turned to gold. The more athletic Aladdin jumps to recover the Hand (using cloth to protect his skin to avoid the same fate that befell Sa'Luk), then returns it to Cassim, remarking to his father that it pays to have a junior partner.
After escaping, Cassim chooses to throw the Hand away, having realized the pain his obsession brought. Although Cassim did not seek vengeance against the Forty Thieves for their betrayal, he unintentionally causes their deaths as the Hand hits their ship, turning it to gold. The solid gold ship proves unseaworthy, and it sinks to the bottom of the sea. Cassim returns to Agrabah with Aladdin, and witnesses Aladdin's wedding from the side. Cassim then accepts Iago as a traveling partner, and the pair travel to see the world.