Vampire thralls are beings that are forcibly under the control of a vampire, and thus possess no free will of their own. They will attack any person or creature, which isn't of the same kind or a vampire, including the Dragonborn on sight.
Be wary, as finding a thrall guarantees that a vampire will be nearby. Based on their armor and their ability to wield weapons and occasionally magic, it can be theorized that they are former bandits or adventurers. Even though the thralls seem to have no free will, they appear to have retained some measure of greed. For instance, in the quest "Laid to Rest," the Dragonborn may see and hear a vampire thrall searching bodies.
In the Dawnguard expansion, if the Dragonborn decides to become a Vampire Lord, more insight into how thralls can be made is revealed. In "Prophet," the Dragonborn is tasked with creating a thrall from a Moth Priest to force him to read an Elder Scroll.
Using Vampire's Seduction on a target (level 10 or lower, once per day) will result to full submission to the vampire. When in state of full submission feeding is allowed, after the feeding process the target can be forged to become a vampire thrall and be commanded to travel to Castle Volkihar for permanent enslavement. Note that if the feeding is not done once Vampire Seduction is used, the target will return to its original state.
Once a Vampire Thrall is created, it will get a series of commands in the speech category. Many of these consist attacking and performing actions. Once a Vampire Thrall is given a command it will be added to its speech list.
- The animation for creating a vampire's thrall (as seen in Dawnguard) is the standard feeding animation.