Vampire

Vampires are a type of monster in myths and folklore (ref here). They are also a type of mutant (ref here), introduced in Fallout 3.

Real Vampires
Vampires exist across the Capital Wasteland and are a type of mutant.(ref here) Though mistaken for cannibals (ref here), they possess several characteristics that humans lack, including sharpened teeth (ref here), enhanced strength and agility (ref here), varying degrees of psychic ability (ref here) and the ability to live off of blood, extracting it from human bodies in a way that leaves the victim alive afterwards (ref here). Though they share their namesake with their fictional counterpart, Vampires lack the ability to transform into bats and are also reflected by mirrors. (ref here)

In the Capital Wasteland, a group formed by Vance named The Family reside inside Meresti Metro Station and have existed for at least six years(ref), with its members originating from various other settlements, such as Rivet City, Megaton and Paradise Falls.(ref) Others have been attracted to the metro station, drawn by the presence of other vampires. Due to Vance's precognition, he has the ability seek out and sense other vampires. (ref) The ideals of The Family were adapted from that of fictional vampires, in order to lay down rules to guide them away from cannibalism, and instead have them act as a civilized group. (ref)

Members of The Family have exhibited numerous unusual feats, including fighting off Enclave patrols single-handedly (ref here), walking from Paradise Falls to Meresti Trainyard while mortally wounded (ref here), living off of only blood packs (ref here), and healing others from near death (ref here). They have also been able to sense another vampire's presence, causing them to seek each other out.(whole lot of refs here) This sense also makes them feel at home when they are together. (ref here) Vance has demonstrated especially strong psychic abilities, even knowing exactly when Ian West would kill his parents, and preparing for it accordingly. (ref here) Ian West also exhibited unusual abilities throughout his life, including tearing the throat out of a cattle thief after being beaten in the head with a club when he was 10 (ref here), and overpowering and killing his parents at 15 with his bare hands. (ref here) Should Arefu and The Family enter a treaty involving Arefu donating blood packs in exchange for the Family's protection, in the form of Alan, Evan King will say that Arefu has never been safer. (ref here)

Perks
The Night Person perk in Fallout 3, Fallout New Vegas, Fallout 4, Fallout 76, and Fallout: The Roleplaying Game, all depict vampires, and provide bonuses to the player only during the night. The Hematophage perk in Fallout 3 also depicts a vampire, and is given to the player by Vance if they befriend The Family, allowing them to heal from consuming blood packs. The Fallout 76 perk Bloodsucker depicts the act of vampirism, and allows the player to heal from blood packs and satisfy their thirst.