Ever since vampire fiction's beginnings with Bram's Stokers original Dracula, there have always been vampire hunters who stalk the night, willing to turn the tables on the blood suckers. Vampire hunters have been just as prolific as vampires themselves, from books to movies, TV shows, video games, anime, etc. These two different types of killers are intertwined in an unending struggle for dominance of the night, but that's not the only interaction between the living and the nocturnal undead. From time to time, a vampire's lust for blood evolves into a lust for flesh - female flesh. Vampires are carnal creatures and they sometimes go into the village their castle looms over and make an impromptu booty call. Thus, the Dhampyr are born.
A Dhampyr, for the uneducated, is the offspring of a vampire father and a human mother (typically, a female vampire doesn't have children, though I don't see that being completely out of the question). In fiction, Dhampyr are typically raised by their human mother, as a vampire has no time to be playing baby daddy. Of course, they still carry a part of their father's legacy (each to a different extent, depending on the story. Some Dhampyr have only a vampire's strengths, while others have only their weaknesses), so they often feel outcast from human society.
Dhampyr usually play a significant role in vampire hunter society. This is mostly because of the prolonged closeness to humans has fostered a kinship toward them and the intimate knowledge of their vampiric legacy show what evil they can be capable of. Due to this, Dhampyr tend to be solitary individuals who hunt their full blooded kin alone, so as to avoid more zealous and closed minded hunters.
Though there are plenty of famous Dhampyr in fiction, I can only think of a few of them right now: The mysterious D from Vampire Hunter D, the luscious Rayne from Bloodrayne (the video games, not the movie - Uwe Boll can suck it), and, the main focus of this post, Alucard, son of Dracula from the Castlevania series.
Alucard was first featured in Castlevania III and became popular enough to warrant his own game, Castlevania: Symphony of the Night. Now all the Castlevania games are classics, but I couldn't play the first three, as they were too damn hard (and platformers, no less). When SOTN came out, it irrevocably changed the franchise. No longer were the stages linear (Though Castlevania II was non-linear, but it was a pain in the ass). You wandered around the rooms of your father's expansive castle, gaining power ups that would allow you to reach other areas. Plus, they implemented a level up system that gave Alucard more hit points to survive the tougher monsters along the way.
The game improved the Castlevania formula by leaps and bounds and has become the new standard in the series. The gameplay was superior, the music was fantastically haunting, and the art style was beautiful. SOTN was the pinnacle of the series. Every good Castlevania game afterward stuck with that formula (By the good ones, I mean the ones on the GBA and DS. All the 3D Castlevanias sucked).
SOTN has been an important part of my Halloween for years. Every October, I pull it out of my box of PS1 games, pop it in the system and soak up all the eerie atmosphere. Vampire hunting never felt so good.