Loissa Felhunter

Loissa Felhunter, or Sarah Smith to the commoner, is a former Burning Legion sorceress and personal ally to Winter Shadowsprye and was a founding member of the Coven of Warlocks in Stormwind.

Early History
Loissa Felhunter (Formerly Smith) was born in Lordaeron City and was quite disillusioned with the whole Holy Light business. When the Cult of the Damned came around, Loissa did listen to their calls, but was apposed to raising the dead to fight enemies. When Lordaeron was sacked, Loissa went south and was located near Dalaran when the Legion was summoned. Loissa was drawn to the power of the Fel and began to learn how to wield it effectively.

Recent History
Loissa was not heard from until the Legion's third and final invasion, where she fought against Azeroth's armies via Fel Fire and Summoning of demons. But after the Tomb of Sargeras was invaded and Kil'jadan was defeated, Loissa saw the chance to go behind enemy lines and made her way to Stormwind. From there, she laid low, abducting one person at a time and did experiments on her, summoning demons or empowering her own power.

Once Loissa learned of the Legion's defeat, she began to make plans to exact her revenge. But she had no real target until she preyed upon Miyu Moonfang as a target. While her initial attempts led to failure and imprisonment, Loissa faked a surrender and managed to take Miyu to her off-world 'lab' after springing a trap. While Miyu was under her control, Loissa inflicted massive pain and suffering, but was not able to break the Kaldorei. Loissa was killed later, but her soulstone was kept safe, allowing for the practically demonic woman to reform in the nether and return.

She was captured by the Rangers and placed in a warded cell, unable to do anything for several days before being released to Winter's care.