King Hassan, titled the First Hassan and revered as the Old Man of the Mountain, established the Hashashin sect as its progenitor, enforcing its doctrines through merciless judgment. His presence lingers in myth rather than history, with no survivors to attest to his interventions—only the certainty that wayward successors meet his blade. He acts as both executioner and purifier, decapitating compromised Hashashin leaders and erasing all traces of his deeds to maintain the order’s secrecy. Clad in armor etched with skeletal motifs and a skull-faced helm radiating eerie blue flames, his visage embodies death’s inevitability. The rusted mantle and rib-like plackart amplify his spectral aura, while pauldrons shaped as skulls underscore his role as an arbiter of mortality. Within the Sixth Singularity, he inhabits the Holy Shrine of Azrael—a gateway to the underworld where only the doomed tread. Rarely, he grants desperate petitioners audience under exacting terms. During the Babylonia conflict, he adopts the mantle of Ziusudra, the flood hero, to test Uruk’s defenders. He later breaches the Underworld to sever Ereshkigal’s pact with the Three Goddess Alliance, intervening without justification. His defining moment arises against Tiamat, a primordial entity untouched by mortality. Sacrificing his Grand Servant status—reserved for humanity’s guardians—he carves the concept of death into her being, cleaving her wings and reducing her Saint Graph to mortal levels. This act enables Chaldea’s victory, showcasing his authority over existential boundaries. His prowess extends to severing intangible forces like telepathic links and unspoken oaths. Rigid in principle, he demands unwavering faith and metes harsh judgment for perceived weakness. Yet pragmatism surfaces when Cursed Arm Hassan bargains his life for Chaldea’s aid. He condemns reliance on external powers as weakness, extolling self-sufficiency as the Hashashin ideal. Despite his severity, he respects figures like Ereshkigal for their dutiful stewardship of the dead, though he refrains from meddling in their affairs. In combat, he forsakes subterfuge, wielding a colossal greatsword with lethal precision. His Noble Phantasm, *Azrael*, erases targets from existence, while *Evening Bell* heralds their demise by weakening resistance to instant death. He channels powers akin to Mystic Eyes of Death Perception, slashing fate’s threads rather than flesh. Enhanced by *Protection of the Faith*, he resists mental assaults and regenerates wounds, while *Battle Continuation* sustains him through mortal injuries. He rebukes later Hassans mercilessly: Cursed Arm for his demon-grafted arm, Hundred Faces for fragmented consciousness, and Serenity for dependence on poison. Each deviation warrants execution, reflecting his dual role as the order’s founder and relentless enforcer of its purity.