Jaffar is the antagonist in Prince of Persia and Prince of Persia 2: The Shadow and the Flame. Jaffar was a traitorous and power-hungry Grand Vizier of the Sultan who intended to marry the the Sultan's daughter to gain power over the Sultan's kingdom, and used magic to accomplish his goals.
Prince of Persia
Jaffar, the Sultan's Grand Vizier wanted very much to marry the Princess. Seizing power, Jaffar had his rival for her affections thrown into the dungeons, but the young man escaped and struck down the evil magician.
When he learned of his Vizier's treachery, the grateful Sultan offered riches but the stranger requested just one reward. And so the young lovers were wed and they lived happily... for eleven days.
The Shadow and the Flame
Jaffar was revived somehow and was out for revenge. He managed to steal the prince's identity and once again seized power over the kingdom. He then trapped the princess in a coma. The Prince eventually manages to kill Jaffar again.