Vlad is an exceptionally powerful vampire who is always found on the first level of Hell at the top of a tall tower.
If killed, he drops his unique cape. Inside a nearby block hides his amulet that grants the Spelunker invulnerability to damage from fire, including lava. It is not necessary to kill him to obtain the amulet.
Vlad is named after Vlad the Impaler - also known as Dracula - who inspired the villain of Bram Stoker's vampire novel. More specifically, it seems likely he is inspired by the version of Vlad in NetHack, who is also a vampire who appears in a tower in the underworld (named Gehennom in NetHack 3.1.0 and Hell in previous versions).
Visually, he resembles Gary Oldman's portrayal of Dracula in the 1992 film directed by Francis Ford Coppola.