Hellsing is a Japanese manga series written and illustrated by Kouta Hirano. It was serialized in Shōnen Gahōsha's seinen manga magazine Young King OURs from April 1997 to September 2008, with its chapters collected in ten tankōbon volumes. The series chronicles the efforts of the mysterious and secret Hellsing Organization as it combats vampires, ghouls, and other supernatural foes who threaten England. The series was licensed for English language release in North America by Dark Horse Comics. From 2002 to 2006, Hirano released a six-chapter prequel series, Hellsing: The Dawn, in Young King OURs Zōkan (later Young King OURs+ before ceasing publication).

A thirteen-episode anime television series adaptation by Gonzo, directed by Umanosuke Iida and Yasunori Urata, with screenplay by Chiaki J. Konaka, was broadcast on Fuji TV from October 2001 to January 2002. A ten-episode original video animation (OVA), titled Hellsing Ultimate, was produced by Geneon. It followed the manga storyline more closely than the anime series. It was released between February 2006 and December 2012. In North America, both the TV series and the OVA were first licensed by Geneon Entertainment and later by Funimation. Following the announcement that Funimation would be unified under the Crunchyroll brand, both Hellsing and Hellsing Ultimate were moved to the platform in 2022.

Hellsing is named after and centered around the Royal Order of Protestant Knights originally led by Abraham Van Helsing. The mission of Hellsing is to search for and destroy the undead and other supernatural forces of evil that threaten the queen and the country. 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 witnessed his death which turned her from a once innocent and shy little girl to a tough and deadly force. She is protected by the faithful Hellsing family butler Walter C. Dornez, a deadly foe in his own right, and Alucard, the original and most powerful vampire, who 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 Nazi Germany 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 lord Alucard, ending a feud begun during World War II.

In 1996, manga author Kouta Hirano published a one-shot titled Hellsing: The Legends of Vampire Hunter in Comic Kairakuten, a hentai magazine issued by Wanimagazine. Hirano later stated that he did not originally intend to create a story in the hentai genre, but rather a "somewhat daring" action narrative. He noted that the one-shot was created quickly, and his ongoing work in hentai facilitated its publication. Subsequently, Hirano developed the concept into a new series, retaining the setting but removing erotic elements to focus on action, which became Hellsing. Due to its unconventional premise, Hirano and publisher Shōnen Gahōsha initially tested reader reception, resulting in a narrative that Hirano described as initially "a little disjointed". After positive feedback, the series was greenlit for serialization.

Hirano aimed to create a story centered on gunplay, but felt that a traditional vampire would be incompatible with firearms. To address this, he redesigned Alucard with a hat and long coat, making him "dark and ominous, but just more suited to his behavior". Hirano emphasized that character design precedes story development for him. He noted that Alucard's design drew comparisons to Vash the Stampede from Trigun (which also ran in Young King OURs), leading him to regret adding sunglasses. To counterbalance the series' dark tone, Hirano introduced Seras Victoria as a female character who could bring warmth and stand out "from the darkness". The numerous references to history, mythology, and pop culture in the series were not based on formal research; Hirano described himself as an otaku who incorporated elements from media he consumed passionately.

For the adaptation Hellsing Ultimate, anime producer Yasuyuki Ueda opted for an original video animation (OVA) format rather than a television series to avoid time constraints. As a fan of the manga, he wanted to thoroughly adapt the source material and believed an OVA offered greater creative freedom. Writer Yōsuke Kuroda agreed to collaborate on the project. Ueda noted that while combining CG with traditional animation was time-consuming, the OVA schedule allowed them to use CG for realistic depictions of weapons and gunfire.

Written and illustrated by Kouta Hirano, Hellsing was serialized for eleven years in Shōnen Gahōsha's seinen manga magazine Young King OURs from April 30, 1997, to September 30, 2008. Its 89 individual chapters were collected by Shōnen Gahōsha in ten tankōbon volumes, released from September 24, 1998, to March 27, 2009.