He watched over the human race and helped prevent the Black Beast from destroying them, as well as sealing Yuuki Terumi inside the Boundary before the Six Heroes were formed. Rachel Alucard is his daughter, and Valkenhayn R. Hellsing served as his butler before (and after) working with the Six Heroes. During the events of Phase 0, Clavis hired Jubei to recover the prime fields, however, the mission failed, resulting in the appearance of the Black Beast. He then ordered Jubei to search for Shūichirō Ayatsuki and to capture him in order to interrogate him. According to Shūichirō's logs, the 'Original Unit' came from the Alucard family.
Clavis appears during Chapter 3: Mitsurugi. At this point in time, he was being hunted down by the Mitsurugi Agency who had hired the Immortal Breaker's own Valkenhayn R. Hellsing and Relius Clover; reason being that Clavis was deemed far too powerful and would need to be managed for the sake of the worlds order.
He appears at Naoto Kurogane's residence where he is treated to some tea by Haruka Hayami. When Naoto arrived with Clavis' daughter, Raquel Alucard, Clavis demanded the she come back with him after putting Haruka to sleep with a form of spell. He asked Naoto how he would feel if Raquel came back with him, to which she objected until Clavis firmly told her in a stern tone that he was speaking to Naoto.
After some time, Raquel attempted to deny Clavis, but to no avail, with him sternly telling her to watch her mouth, with this, he reached for her hand to only have it slapped away by Naoto with a comment about how self-centered he was acting; to this, Clavis apologized but cut off Naoto's arm.
After cutting off Naoto's arm, he noticed how it was made out of his daughters blood, stating that while it wasn't bad, it could be improved on; with this, he forged a new arm for Naoto out of his own blood. While creating this arm, he asked Raquel why she chose Naoto and said to the boy that, should he desire, he could temporarily leave her in his hands for the time-being.
Very soon afterwards, Valkenhayn bursted through the door and exclaimed that he had finally found Clavis, to this, Clavis told Naoto as a thanks for the tea, he will not allow the kitchen to come to any harm. Valkenhayn leapt to Clavis and bit his arm, to which Clavis raised his arm and gazed at his future butler, saying it had been a great many years since he had seen a lycanthrope with his own two eyes. After Relius joined the battle, Clavis decided it would be wise to leave and fled with the duo on hot pursuit. After the battle, Naoto was amazed to find some specific parts of the apartment in the same state it was before Clavis arrived while other places were in complete ruin.
He appeared as an elderly man in a wheelchair, with long, white hair and beard, and red eyes. He wore a floor-length black, red and gold robe with a high collar, which was covered by a cloak.
- There is a translation error in the American and European versions. The English script reads his name as Claudius, but the voice acting pronounces it as Clavis.