"Medivh, the Last Guardian, made his home in Deadwind Pass, in the bright tower of Karazhan. Though he was the greatest wizard of his day (and humanity's intended custodian) Medivh was secretly possessed by the dark spirit of Sargeras, the Destroyer of Worlds. Through Medivh, Sargeras opened the Dark Portal and allowed the orcs to wage war upon the kingdoms of Azeroth.As the war progressed, Medivh fought against Sargeras' control. The raging conflict within him finally drove the wizard irrevocably insane, until his childhood friend, Anduin Lothar, aided Medivh's young apprentice, Khadgar in storming Karazhan and slaying their former comrade. Since that day, a terrible curse has pervaded both the tower and the lands around it - casting a dark pall over Deadwind Pass and the region that is now known as Duskwood.
In recent years, nobles of Darkshire ventured into Deadwind Pass to investigate the blight that had settled over the region. None who entered the dark tower ever emerged."
via Battle.net 