Not one of the harder quest nemeses, Count Dracula respects Elbereth and has no magic capabilities. Although he has a level-drain attack, as an Undead Slayer you will automatically be immune to this ability. However, there is a risk that among Dracula's bodyguards there will be a vampire mage capable of casting summon nasties and various other dangerous spells. This can present a major challenge to a level 12 or 13 character. On the other hand, with conflict, you can use those monsters against Dracula himself, potentially destroying him without waking him up yourself.
He is based on the non-fictional Vlad Drăculea, a 15th century Romanian prince. Strangely enough, the unique monster Vlad the Impaler is also based on Drăculea. Count Dracula's last words ("Mark my words, niggling! I shall return!") imply that they may be intended to be one and the same, though.
The Undead Slayer quest nemesis has changed several times since the role's first appearance in NetHack Plus. In that variant, the nemesis was "Master Vecna", a weaker early version of SLASH'EM's Vecna.
In SLASH 6, the nemesis was "Lord Vlad the Impaler", with stats almost identical to those of Count Dracula, except that he lacked a level-draining bite attack, and appeared as @ instead of a vampire. Vlad the Impaler, as guardian of the Candelabrum of Invocation, was also present in this variant, with no explanation given as to why the Undead Slayer had to fight him twice, other than the Quest version having the same last words as mentioned above.