"I am Cairo of the Bright Circle...Cairo, daughter of Mek...Cairo the Master!"— Cairo(src)
Cairo is a Master Necromancer.
Cairo's breathren were slain by demons when she was a girl. She spent years planning her revenge, and discovered the legend of the Hand of Naz, an artifact within the castle of Kanemith that could supposedly raise a spectral army to do the wearer's bidding. However, it could only be worn once, and Cairo suspected that using it would carry a price. She also knew that the gauntlet was guarded by undead. Nonetheless, she traveled to Daken-Shar, where the gauntlet lay within a tomb.
During this time, Baal's Army of Destruction were making headway against the Barbarians in his march to Mount Arreat. Cairo witnessed a Barbarian army be besieged by his demons. Only one Barbarian survived the battle—Renit the Dark Stalker. Seeing an opportunity, Cairo planned to use the warrior as a pawn, to get him to wear the gauntlet and see for herself what would happen. To this end, she presented herself as being a Necromancer of little power, calling for aid within a tower at the sight of spiders. Cairo could see Renit's lust for vengeance and told him that her breathren had been slain (a truth, but claiming that it had happened recently rather than years ago). She told him of the Hand, and how it could be used to defeat their common enemy.
Cairo led Renit to Kanemith, where they entered a tomb beneath the castle, finding the gauntlet worn by a long dead king. At this point a horde of skeletons crawled out from the ground. Renit fled with the gauntlet, leaving Cairo to die. Cairo had planned for this and escaped, and saw Renit use the gauntlet against a group of demons, summoning his spectral army to his side. She watched as the spectres slew the demons, after which the king slew Renit, and she realized the truth - the price for using the Hand was to be added to the army.
Cairo revived Renit and revealed her deceptions. Unfazed by his anger, she destroyed the Jewel of Naz (a component of the gauntlet), releasing the spirits to the afterlife, but gaining their knowledge. In her eyes, this was the true prize. With that done, she rode off, telling Renit that they would not meet again.