Dracula
Dracula was the historical Vlad Ţepeş. He claimed to have killed more people than God’s plagues combined before he was ever a vampire, and made reference to impaling people in times past (such as those who failed to show him deference, for example).

He met and “hung out” with Anyanka, a vengeance demon and Patron Saint of Scorned Women, when she was about 700 years old. Anyanka had cursed a man by making him incredibly obese, and Dracula complimented her by saying that the man was doomed forever.

In 2000, Dracula came to Sunnydale, a Californian town which lay on a Hellmouth and was home to Buffy Summers. He had heard the stories about the world-famous Slayer and had made up his mind to meet her face to face. After introducing himself to the starstruck “Scooby Gang” (as Buffy and her friends called themselves), Dracula hypnotized Buffy’s friend Xander Harris into becoming his servant and later seduced Buffy into letting him bite her whilst in her bed. Xander eventually led Buffy to Dracula’s castle on the outskirts of Sunnydale, where she tried to take control and kill him, but once again fell victim to his “thrall”. After willingly beginning to drink Dracula’s blood, Buffy was at first surprised and remarked “Wow”.

However, she soon regained her senses and battled the vampire, staking him. Upon her apparent departure, Dracula tried to reform from mist, but Buffy reappeared and staked him a second time, telling him she was wise to his tricks, having seen his movies. When he again tried to reform, she reminded him that she was still there and would just stake him again if he came back. Finally, accepting that the Slayer was too strong for him, Dracula left Sunnydale.

Buffy: (to Dracula after staking him a second time) You think I don’t watch your movies? You always come back.
~Buffy Summers to Dracula (5x01; Buffy vs Dracula)

In the Buffyverse, Dracula is shown to be different from the Hellmouth vampires found in Sunnydale. While the Hellmouth vampires have the ridged forehead and the yellow eyes (which is what Buffy refers to as the “game face”), Dracula is quite unique in that he has a human face and perpetual fangs.

Also, because of his shape-shifting abilities, Dracula is able to feed without slipping into the “game face” of the Hellmouth vampires, especially the ones that Buffy fought and dusted. Spike explained Dracula’s having that ability as “gypsy magic”.

Just imagine what could happen if one of the Hellmouth vampires (such as Lyle or Tector Gorch, for example) caught Dracula in the act of feeding off of someone (especially if Dracula’s victim happened to be a criminal, such as a mugger, or even a rapist, too).

Just think of the possibilities… ;)

Plus, I can see Caleb suddenly encountering Dracula in Restfield Cemetery, the same way Buffy did in the Season 5 episode Buffy vs. Dracula, and the ensuing conversation going something like this – only different, though, since it pertains to Caleb, of course:

Caleb: Who are you?
Dracula: I apologize. I assumed you knew. I am Dracula.
Caleb: Get out! (a few seconds later) So let me get this straight. You’re… Dracula. The guy. The count.
Dracula: You know who I am. As I would know without question that you are Caleb, the ex-preacher and serial killer. (Caleb looks surprised at Dracula knowing his name. Dracula steps over to Caleb, looming over him) I have searched the world over for you. I have yearned for you… for a creature whose darkness rivals my own. (He runs his fingers over Caleb’s cheek.) The hits from your father… those nights when you would listen to them fight as a child while hiding in your bedroom… you remember.
Caleb: No. (Dracula then puts his hand behind Caleb’s neck)
Dracula: Do not fight me, Caleb. I can sense my manservant Xander’s cry for vengeance. And I will seek that for his sake, as well as for what you did to him. (Pauses) Taking one of his eyes like that. I am very much displeased. (Dracula then leans down to bite Caleb’s neck. Caleb gasps but is unable to pull away.)

From my perspective, Rudolf Martin is a fantastic actor, and he did a great job bringing Dracula to life the way he did on the show as well. However, it is too bad that Dracula only appeared in one episode, because not only could he have been a great ally for the Scooby Gang), but he would have also made a great friend to Xander too.

And speaking of being a great ally, Dracula would have helped them out with Glorificus much earlier than in canon by first drinking some of Buffy’s blood and then jumping into the portal in Buffy’s place, which would have saved Buffy the trouble of closing the portal herself. Of course, as Dracula, being a vampire, is one of the undead, the portal would’ve been unable to kill him anyway, and he would have survived.

As for helping Buffy, Dawn and the Scoobies out with the problems caused by the nerd Trio in Season 6, Dracula would’ve stopped Warren from shooting Buffy with a gun (and indirectly causing Tara to be hit with one of the stray bullets). He would’ve accomplished that by either making it so the bullet meant for Buffy instead hits Warren in the heart, making him die from blood loss, or impaling Warren on a tall version of the wooden stake Buffy would use to dust the Hellmouth vampires, thus causing a shocked Buffy and Xander to realize why Dracula was also called “Vlad the Impaler”.

When it came to Caleb and the First Evil in Season 7, Dracula again would have been a great help, especially with taking down the Harbringers of Death (aka Bringers) and then helping potential Slayer Chloe in having more self-confidence so that she never commits suicide. (Of course, Dracula appearing to Kennedy and telling her where she can get off would be a plus as well.) During the battle with Caleb, Dracula would have stopped him from taking an eye belonging to Xander, and telling him that “nobody steals from [Dracula]”, before immediately draining Caleb of his blood.

Finally, as for the First Evil, Dracula would have caused the Turok-Han vampires to be instantly dusted (without the aid of sunlight), which would have caused the First Evil to become powerless (as destroying its army effectively rendered it to be so).
A mysterious smile
Sensing a presence