Hellsing is named after and centered around the Holy Order of Protestant Knights, originally led by Abraham Van Helsing. The mission of Hellsing is to protect Queen and Country from the undead and other supernatural forces of evil. This organization is currently led by Sir Integra Fairbrook Wingates Hellsing, who inherited the leadership of Hellsing as a child after the death of her father. She is protected by the faithful Hellsing family butler and former Hellsing "trashman," Walter C. Dornez, and Alucard, the original and most powerful vampire that swore loyalty to the Hellsing family after being defeated by Van Helsing one hundred years before the story takes place. These formidable guardians are joined early on in the storyline by former police officer Seras Victoria, whom Alucard turned into a vampire.
As the scale and frequency of incidents involving the undead escalate in England and all around the world, Sir Integra discovers that the remnants of a Nazi group called Millennium still exist and are intent on reviving the Third Reich by creating a battalion of vampires. Millennium, Hellsing, and the Vatican section XIII Iscariot clash in an apocalyptic three-sided war in London, and Millennium reveals its true objective: to destroy the vampire Alucard, ending a feud begun during World War II.