Vampires

Vampires are the creatures of the night and can give you a disease called Vampirism, this disease turns you into a vampire.

Harkon (pure-blood vampire)

But in the Dawnguard expansion you meet the few pure-blood vampires, the head pure-blood vampire is called Harkon and he gives you an option when you first meet him. Join or be pray.

Vampire Lord

This expansion allows the player to transform into a Vampire Lord (but only when turned by a vampire lord). the new transformation even as its own skill tree which you level up by killing people in different ways. The skills in the skill tree vary for senses to movement as well as magic related skills.

Vampire Skill Tree