The Dhampirs are children of one vampire parent and one human parent, with all the strengths of vampires, and, save the thirst for blood, few or none of their weaknesses (Alucard, while seen breathing, lacks a reflection and is hurt by water without the right relics in Symphony of the Night). Certain sources indicate that even the thirst for blood do not carry on to the dhampir children.
According to lore, dhampirs were very useful to the superstitious community because, being part vampires, they could recognize another vampire, even if they were invisible or had transformed into an animal. A town would hire them to find and kill a vampire, for a fee of course. Much of the time, the dhampir could talk to the vampire and convince them to leave. Some dhampirs resent their vampiric lineage and act as human hunters do, going on a campaign to kill the vampire that seems to be causing trouble. Dhampirs that follow this path in life would join gangs of hunters to track down vampires, and even their own family in some instances. Naturally, the human hunters were more than pleased for gaining an immortal member with inside information.