Dark magic users were those people who were able to weave various dark spells. Galbatorix was a prominent dark magic user, and it is presumed he taught some to Murtagh as well. Dark magic users were able to manipulate the minds of living beings with this magic.
Forbidden magic[]
The Riders were strictly forbidden to manipulate dark magic.
Other users of dark magic[]
Other users of dark magic included Shades such as Durza and Varaug. Murtagh also has the ability to cast dark spells.
The Black Hand[]
The Black Hand was an organization which worked for the Empire. Drail was one of the Black Hand who was also able to use dark magic to almost assassinate Nasuada.