Vampire's Servant is one of the Powers you receive as you progress as a Vampire. It allows you to reanimate a very powerful body to fight alongside you for 60 seconds. As a Power it can only be used once per day.
Unlike necromancy spells of the Conjuration spell tree the victims of Vampire's servant do not turn to ash when the effect wears off (Except on stage one of vampirism). It's similar to Dead Thrall of the conjuration tree but you can target every dead corpse. Unfortunately the effect wears off after 60 seconds. So it's sort of a thrall: At the moment of casting more powerful (as you can raise whatever creature you want) but much less effective for long fights.
Needs further testing but apparently, the perk Necromage does not influence the duration of this Power, unlike spells of the conjuration tree.
[000ED0A4] Stage one: Reanimate a body for 60 seconds, max level: 6, becomes ash when killed.
[000ED0A5] Stage two: Reanimate a body for 60 seconds, max level: 13.
[000ED0A6] Stage three: Reanimate a body for 60 seconds, max level: 21.
[000ED0A7] Stage four: Reanimate a body for 60 seconds, max level: 30, fortify heal rate by 1 (doesn't seem to do anything).
- The Elder Scrolls V: Skyrim (First appearance)