Jafar was one of the greatest foes of Aladdin.
Once the Grand Vizier of Agrabah, Jafar was the Sultan most trusted advisor, as well as a minor sorceror. His only confidant was his parrot, Iago. Jafar was not content with being merely the Vizier- he desired to overthrow the Sultan and become the most powerful sorceror in the world. To do this he spent many years studying and searching for the Cave of Wonders and the Genie of the Lamp within. At some point he acquired half of a magical scarab, and hired a thief to find the other half. Upon receiving the other half, Jafar combined them and chased the scarab to the Cave of Wonders. He sent the thief in, only to have him devoured. Jafar needed to find the "Diamond in the Rough", the only one who could safely enter the Cave. He used his snake-staff to hypnotize the Sultan into giving him his ring, with its mystic blue diamond, which he used to learn the "Diamond in the Rough"'s identity- a common "street rat" named Aladdin. He sent the royal guard to arrest Aladdin.
Jafar disguised himself as an old man and snuck into the dungeon, and made a deal with the young thief, promising him riches in exchange for getting him the lamp. Aladdin agreed, and as he found the lamp, his monkey Abu touched the treasure, causing the Cave to collapse in on him. Aladdin almost escaped, and Jafar demanded Aladdin throw him the lamp. He did, so Jafar decided to give him his reward, and prepared to stab him. Abu bit Jafar and stole the lamp as the Cave collapsed. A frustrated Jafar returned to the palace, without the lamp. He knew that his days were numbered, as Princess Jasmine would soon be queen, and once she was she fully intended to get rid of him.
Fearing banishment or death, Jafar needed to find a new means to be Sultan, and Iago suggested he marry the Princess and become Sultan. Jafar agreed, feeling the idea had merit, fully intending to drop both the Sultan and Jasmine off a cliff once the deal was done. He found an old law saying if a suitable prince could not be found, the princess must then marry the Royal Vizier, and attempted to hypnotize the Sultan into arranging the marriage. His plot was interrupted by the arrival of "Prince Ali Ababwah," who had come to try and marry Jasmine. Jafar was suspicious of him and made little effort to hide it. While Jasmine rejected Ali at first, Jafar decided not to take any chances and hired Razoul and the palace guard to kill him. Once that was done, Jafar hypnotized the Sultan and was prepared to marry Jasmine. His plan was ruined by the miraculous return of Ali who confronted Jafar about the attempted murder. In a panic, Jafar tried to again hypnotize the Sultan into believing Ali was lying. However, Ali destroyed the snake-staff, and the Sultan saw Jafar for the traitor he was. As the Sultan called the guards, Jafar caught a glimpse of the magic lamp in Ali's clothing and escaped in a cloud of smoke.
Jafar realized Ali and Aladdin were one and the same, so Jafar had Iago steal the lamp. Jafar summoned the genie and made his first wish to "rule on high as Sultan!" The wish was granted, but when Jasmine and the Sultan refused to bow to Jafar, he decided that if they would not bow before a Sultan, than they would cower before a sorceror. Thus, he made his second wish "to be the most powerful sorceror in the world!" It was granted and he proceeded to taunt and humiliate his enemies. He unmasked Ali as the street rat Aladdin and banished him to the ends of the earth, before truly beginning his new reign of terror.
Jafar now had it all, but he wanted one more thing- Jasmine as his queen. She refused his proposal, and not knowing the Genie's rules, Jafar wished that Princess Jasmine would fall desperately in love with him. By that point Aladdin had returned and in order to distract Jafar, Jasmine pretended that his wish had worked to buy time for Aladdin to steal the lamp. Jafar quickly saw through the ploy, just in time to prevent Aladdin from succeeding. The two adversaries engaged in a fierce combat, which climaxed when Jafar transformed into a gigantic cobra. Aladdin was no match for the sorceror, but by then he had figured out Jafar's true weakness- his lust for power. Aladdin taunted him by telling him "the genie has more power than you'll ever have, he gave you your power. He can take it away!" Jafar realized Aladdin was right and fully intended to to something about it. He made his third wish to be an "all powerful genie!" The wish was granted and Jafar was prepared to rule the entire universe, but then Aladdin pointed out his folly. With the wish came the price- Jafar was a slave to the lamp- and Aladdin imprisoned both him and Iago in it. Jafar was defeated. The Genie threw the lamp into the Cave of Wonders, where he was to remain forever imprisoned.
However, it was not to last. Weeks later, Iago had dug out of the Cave, dragging the lamp with him. However, upon being insulted by Jafar, Iago dropped his lamp into a well and took off for Agrabah himself. Jafar was found that night by the thief Abis Mal, and Jafar was able to take advantage of him easily after conning him out of his first two wishes. Abis Mal had too been humiliated by Aladdin, and Jafar decided to use him to take revenge. They journeyed to Agrabah, where Jafar learned that Iago managed to get in good with Aladdin and Jasmine, which served his plans perfectly. He approached Iago and intimidated him into arranging a trap for Aladdin and the Sultan, while Jafar captured the Genie and Abu. Afterwards, in the form of several horseman, Jafar (along with Abis Mal) kidnapped the Sultan and Carpet, leaving Aladdin stranded in the desert. Before Aladdin could arrive return to the palace, Jafar captured Jasmine and arranged for Aladdin to be framed for the murder of the Sultan. Disguised as Jasmine, he sentenced Aladdin to death at sunrise.
Thinking his plan worked and he was finally in control, Jafar attempted to get Abis Mal to free him from the lamp, when bribing him didn't work, he turned to intimidation, long enough for Aladdin to get the lamp away from Abis Mal. Jafar blasted him and attempted to destroy his enemies once and for all to protect his lamp, eventually turning the palace courtyard into a sea of lava. Aladdin could not get close enough to grab Jafar's lamp, so Iago truly betrayed Jafar and kicked his lamp into the lava. With the lamp destroyed, Jafar was also destroyed.
Or so everyone thought. Upon arriving at the Underworld, Jafar was able to intimidate the two imps, Pain and Panic, into bringing their master Hades to him. Jafar appealed to Hades to grant him life once more, but Hades ignored him. Jafar approached Hades again and caught him scheming how to overthrow Zeus, seeing someone who finally understood his frustrations. Hades and Jafar began exchanging stories about their plans and their arch-enemies. Jafar boasted that he could easily defeat a "muscle-bound ox like Hercules" and Hades decided to give Jafar a chance to back it up. He restored Jafar to life and granted him new magic powers tied to his staff, sending him after Hercules. While the sorceror came close to defeating him, Jafar was overwhelmed, never having dealt with such strength when battling mortals. Hades boasted that a mere mortal like Aladdin was child's play, and Jafar challenged him to take the hero on. Hades agreed and sent Pain and Panic to do it. Predictably, they failed, and Jafar posed a new plan- get Hercules and Aladdin to destroy each other.
Jafar kidnapped Abu and Hades captured Icarus, and managed to manpulate both heroes into believing the other was the kidnapper. After seemingly killing one other, Aladdin and Hercules realized they'd been played, and who played them. With Hercules out of the way, Hades was prepared to conquer Olympus with Jafar as his ally, and once that was over he'd reward Jafar by making him the new god of the Underworld. Jafar found the idea intriguing. At that moment, Hercules and Aladdin attacked the Underworld, and Jafar was sent out to destroy them. However, the heroes had disguised themselves as one other, causing Jafar to use the wrong tactics on each. They destroyed his staff- and with the staff gone, Jafar was returned to being a mere spirit, dragged into the River Styx.
Jafar appeared as an ally of Maleficent as part of a plot to use the Heartless to conquer all the different parallel worlds. Jafar captured Princess Jasmine and took control of the Genie but was defeated by Sora, Aladdin, Goofy and Donald Duck. He was reimprisoned in the lamp.
In the comic book The Return of Aladdin, released before the Disney TV series began, Jafar escaped the Cave of Wonders in more or less the same way as in the main history. However, Iago remained loyal, Jafar's pawn was a stage magician (not a true sorcerer), and Jafar and Iago were re-imprisoned at the end.