Father Alexander Anderson is a major figure within the Iscariot Organization, the secret execution arm of the Vatican. His primary role is that of a paladin, a monster hunter and vampire purifier, and he is widely considered Iscariot's most powerful asset, often referred to as its trump card. He resides in Italy, where he operates an orphanage on the outskirts of Vatican City, a detail that contrasts sharply with his violent profession. In English adaptations, he is often portrayed with a Scottish accent, though his canonical nationality is not explicitly defined.

Physically, Anderson is an imposing figure, standing well over two meters tall with a lean but broad-shouldered build. He has short, spiky blond hair, green eyes, and tanned, weathered skin. A large, wedge-shaped scar is permanently etched on his left cheek. His attire is a priest's cassock, typically grey with specific trim depending on the adaptation, worn over a dark suit and shirt with a clerical collar. He wears white gloves marked with religious inscriptions, such as Jesus Christ is in Heaven on the right hand and Speak with the Dead on the left, and carries a silver cross around his neck.

The personality of Alexander Anderson is defined by a sharp duality. Outside of combat, he is calm, collected, and surprisingly gentle, showing genuine kindness and care toward the orphans under his protection. In battle, however, he undergoes a dramatic transformation, becoming merciless, ferocious, and almost unstoppable. He has a habit of hissing and laughing wildly during fights, losing himself in the thrill of the hunt in a manner that mirrors his arch-rival, Alucard. Despite this frenzy, he possesses a strong sense of focus and self-restraint, especially when the safety of innocents or his own moral code is at stake.

Anderson is an ardent and fanatical Catholic. He compulsively quotes scripture, framing his violent crusade as a direct extension of the word of God. His initial portrayal reveals a deep-seated hatred for Protestants and non-believers, referring to Integra Hellsing as Babylon and expressing resentment over English control of Northern Ireland, which he views as Catholic territory. However, as events unfold, his character reveals greater complexity. While his mission is to destroy the monsters of the Hellsing Organization, his motivations are not merely based on blind hatred. He is driven by a genuine, if twisted, sense of righteous duty to protect humanity and the Catholic faith from supernatural threats.

Within the story, Anderson serves as the primary rival and foil to Alucard, the Hellsing Organization's most powerful vampire. Their first encounter is a brutal clash that establishes their enduring and complex relationship. Anderson's key relationship within Iscariot is with Enrico Maxwell, the organization's leader. He initially follows Maxwell's orders but eventually turns against him when Maxwell becomes intoxicated by power and begins a genocidal crusade against innocent humans, showing that Anderson's loyalty to his faith and moral principles supersedes his loyalty to a corrupt superior. He also develops a begrudging respect for Integra Hellsing, admiring her conviction and bravery to the point of escorting her personally to safety, a gesture of gentlemanly respect that surprises even his own allies. He acknowledges Seras Victoria's transformation and strength, treating her with a level of recognition rather than simple contempt.

The character of Alexander Anderson undergoes a significant development arc. He begins as a seemingly one-dimensional, fanatical antagonist but evolves into a more tragic and honorable figure. His growing disillusionment with Maxwell's extremism culminates in his direct intervention to stop the massacre of innocents. His rivalry with Alucard deepens into a form of mutual respect; Alucard even compares Anderson to Abraham Van Helsing and the other men who first defeated Dracula, acknowledging that a true human with an unbreakable will is the only being worthy of killing a monster. This respect turns to profound disappointment in their final confrontation. To match Alucard's overwhelming power, Anderson uses the Nail of Helena, a holy relic said to have pierced Christ's body. By impaling his own heart with the nail, he sacrifices his humanity to become a monstrous, plant-like being. Alucard, who had looked forward to dying at the hands of a worthy human, now sees Anderson as just another monster. In his final moments, as he dies from the nail's removal, Anderson consoles his grieving rival, telling him that monsters do not cry, thereby reclaiming a shred of his humanity in death.

Anderson's abilities are far beyond those of a normal human, owing to his status as a Regenerator, a genetically modified superhuman. He possesses immense superhuman strength, capable of staggering Alucard with a punch and slicing through steel. His speed and reflexes are sufficient to dodge bullets and catch even Alucard off guard. His most famous weapon is an effectively limitless supply of blessed silver bayonets. He wields these with supernatural accuracy, throwing them with enough force to impale vampires through walls and across great distances. He is also highly skilled in close-quarters combat, using the bayonets as swords. His signature ability is his rapid regenerative healing factor, allowing him to survive gunshots to the head and the loss of limbs, continuing to fight through wounds that would be instantly fatal to anyone else. He can also use pages of scripture to create holy barriers that can trap or repel supernatural creatures. Upon using the Nail of Helena, his power increases exponentially, transforming his body into a mass of holy thorns with an even more potent healing factor, but at the total cost of his human identity and sanity.