All death knights can learn to exude a dark, raging battle aura that causes allied creatures around them to move and regenerate life more quickly.WC3Man 38
Before Wrath of the Lich King
Prior to WotLK, Unholy Aura was possessed by death knight bosses such as Baron Rivendare. It did about 150 damage every 2 seconds to anyone in range.
Patch changes
Patch 5.0.4 (28 August 2012): Re-added; changed from All party or raid members within 45 yards of the Death Knight move X% faster. This effect does not stack with other movement improving effects.
Patch 3.1.0 (14-Apr-2009): Replaced with Improved Unholy Presence. Allows the death knight to keep the movement speed bonus of Unholy Presence in any presence, and increases rune regeneration rate while in Unholy Presence.