Marcellus is a character from the Onimusha series where he is the demon boss in Onimusha: Warlords. He was once an Oni Warrior that was converted into a Genma through Guildenstern's experimentation. This engineered demon, created from materials fetched from the Cave of Treachery, is Guildenstern's pride and joy. He wields a weapon resembling the Oni Gauntlet on his right arm.
Over a 100 years ago during the prolonged brutal warfare between the saintly Oni Clan and the evil Demon/Genma Race called the Oni War, Marcellus, a warrior monk formerly known as Murokoto, had long been a legendary Oni warrior. He fought alongside another Oni warrior called Sougen in this prolonged brutal battle, earning the glory of his unique combat-skill by striking fear into the heart of every Genma battalion with possession of the bestowed divine orb of wind element, Arashi. His existence now perceived as a threat to the Demon Clan, he caught the attention of the Demon Lord Fortinbras and his trusted minion, the Demon Scientist Guildenstern, who then plotted his demise. This resulted in the horrific murder of the Oni Warrior, who accepted a duel challenged by Guildenstern, which turned out to be a setup by the demon scientist himself.
However, Murokoto's soul wasn't put to rest for good. His lifeless corpse eventually fell into the hands of the Genmas. Thanks to the plotting scheme of the insidious Guildenstern, Murokoto's corpse was experimented on and eventually resurrected into a mindless undead, only doing bidding to the Demon Lord. He was then renamed Marcellus, which means "Ultimate Warrior Of The Genma Legion", and was the most valuable asset of the Genma clan. They manipulated Marcellus against his own race, the Oni Clan, to whom he had sworn allegiance.
Marcellus made his debut by battling Samanosuke Akechi in Onimusha: Warlords, as ordered by Guildenstern himself. However, due to his persistance and battle prowess, Marcellus was eventually defeated and vanquished, and his warrior orb of wind, Arashi, ultimately fell into the hands of Samanosuke. Nonetheless, he was resurrected again with new powers, but Samanosuke came out on top and he was defeated once more.
In Onimusha 3: Demon Siege, Marcellus was revived a third time, but he was much weaker this time. He was encountered twice by Jacques Blanc, who tried to stop him from reaching the new Genma Lord Nobunaga, and was eventually defeated in their duel.
Once again, Marcellus made his fourth and last appearance, when he was revived, attempting to stop Soki from escaping the Oni Mansion. He was eventually vanquished by Soki after he went into Onimusha Form.
- Man Killer - Marcellus' weapon when first encountered in Warlords. It is a large sword designed to sever the limbs of opponents. It was forged from the Arashi when he was still in possesion of it and has the power of wind.
- Horse Killer - (only in Blade Warriors) - A signle-edged sword which is an even larger version of the Man Killer.
- Oni Splitter - (only in Blade Warriors) - A treasured axe passed down through generations of demons.
- Extinction - Marcellus' weapons used in the second encounter in Warlords, these twin swords were forged in the demon's world.
- Despair - (only in Blade Warriors) - These twin swords have absorbed the souls of every foe they have cut down.
- Claymore - (only in Blade Warriors) - Legend has it this giant sword was used by a Scottish hero.