Linnena Hallow studied magic from an early age, having been dumped on the doorstep of a mage's house in Stormwind as a child. Having no chldren and being raised among mages, she grew to be talented and cold. From an early age she had been contacted by Kel'Thuzad as he sowed the first seeds of the Plague of Undeath through Stratholme. She was instrumental in raising the undead army to strengthen the Scourge. With that done, she began training necromancers to further serve the Scourge.
She has met with some resistance, as the Forsaken do what they can to stop her. The Forsaken are desperate for the powers of a necromancer, and they focus on the trainees to try entice them to their side. However, the Scourge has so much more to offer a necromancer, and most of them serve Arthas Menethil. With Linnena training them, they become as cold and calculating as she is.
Her whereabouts are unknown, but she is rumored to be alive and well, and that she is wandering around somewhere in the Southern Lordaeron, and some even says that she may be in the Hinterlands, to try raise either the forest trolls or the Green Dragons. ( )