Dracula was a vampire of unknown (presumably Eastern-European) origins, who was the inspiration for the Bram Stoker character. He had a number of powers not standard for vampires of his world, such as being able to transform into a mist or a bat, the ability to mesmerize and control people's minds, and the ability to resurrect himself after he has been turned to dust. Dracula had met up with both Spike, (who considered him a 'drama queen') and Anya (who considered him 'cool') at some point in the past.
The vampire came to Sunnydale, drawn there by tales of the Slayer, Buffy Summers. He purchased a castle just outside town, and attempted to seduce Buffy into joining him as a vampire. He also made Xander his slave. Dracula nearly succeeded in attracting Buffy to his side, appealing to her darker nature, but her stronger Slayer nature broke her free from his control and she defeated him.
Dracula returned, and took Xander as his manservant once more, keeping him at his castle for an entire year. During that time, Dracula came to see Xander as something of a friend. However, Xander was ultimately freed by Buffy.