Durza

An explosion split the air. A long slab of the chamber floor buckled and blew thirty feet up. Needles of rocks flew outward as it crashed down. Eragon stumbled back, stunned, groping for Zar’roc. The twisted shapes of Urgals clambered out of the hole in the floor.

Eragon hesitated. Should he flee? Or should he stay and try to close the tunnel? Even if he managed to seal it before the Urgals attacked him, what if Tronjheim was already breached elsewhere? He could not find all the places in time to prevent the city-mountain from being captured.But if I run to one of Tronjheim’s gates and blast it open, the Varden could retake Tronjheim without having to siege it. Before he could decide, a tall man garbed entirely in black armor emerged from the tunnel and looked directly at him.

It was Durza.

Battle at Farthen Dur, Eragon, pg 707