Marcus came to him willingly and became Chen Mo's new subordinate.
He asked Chen Mo to help him find his twin brother — William, the origin of the werewolf plague and the progenitor of the werewolves — and asked Chen Mo to grant them shelter, a place to survive.
For many years, although he and William possessed immortal bodies and great power, they had always been regarded as abominations by humans, who sought to exterminate them.
Marcus himself had to hide by day and only dared move at night, always keeping clear of human eyes for fear of being discovered.
He had lived like that for countless years.
In Marcus's view, werewolves and vampires should be the true rulers of the Earth. They were powerful and immortal — the most perfect beings in the world — and thus should hold dominion over it.
Now he saw in Chen Mo an opportunity to rule. With the enormous power Chen Mo commanded, if all his knights were turned into vampires, the world would sooner or later fall under their rule.
Then Marcus, progenitor of the vampires, could stand at the peak of the world. No more hiding, no more scurrying through the shadows — all humans would become their slaves; vampires would be the true rulers of the earth.
Marcus had not waited, as in the movie, to tempt Chen Mo with immortality only when Chen Mo was old or dying; Chen Mo's power was simply too great already. Beyond the astonishing strength Marcus had witnessed, the knight order Chen Mo commanded was far stronger than Victor's force decades later in the film.
Marcus feared that if he delayed, William might be killed by Chen Mo or Chen Mo's knights.
He also needed Chen Mo's help to control the ever-increasing werewolf population; otherwise those beasts would destroy the world.
When Marcus first saw Chen Mo summon thunder and burn the werewolves to ash, he had been stunned and treated Chen Mo like a god.
But after the initial shock and some calm reflection, he grew suspicious.
If Chen Mo were truly a god, he could have wiped out every werewolf at once — there would have been no need to kill them one by one and risk losses among the knights. From that, Marcus concluded Chen Mo was not a deity, at most another "other" like himself — a being with extraordinary powers.
In a sense, compared with ordinary humans, they were kin.
For William's safety and for his own ambitions, Marcus chose to approach Chen Mo and successfully join his ranks.
When Chen Mo called his name aloud, Marcus guessed Chen Mo probably learned it from his sire — after all, only that being who had given Marcus and William their strange blood should know his name.
Marcus did not know that Chen Mo, though he had never met that sire, had been searching for him all along.
The first immortal in the world — Alexander Kervinas.
Alexander Kervinas, a fifth-century Hungarian warlord. A sweeping plague ravaged his lands; he alone survived.
It turned out he was born different — possessing the "perfect blood."
This perfect blood could merge with any genome to strengthen itself. It lay dormant until the plague virus awakened the ability, allowing him to survive and then evolve into the very first immortal.
Three of his children inherited this strange constitution. Marcus and William were bitten by a bat and a wolf respectively; after merging with the bat virus and the rabies-like lycanthropic pathogen, each underwent their own evolution — becoming the progenitors of vampires and werewolves.
Vampires and werewolves were both immortal, but each had fatal weaknesses: vampires feared sunlight; werewolves feared silver.
Both sons became voraciously bloodthirsty. Marcus required blood to sustain life, while William lost all reason and became a mindless beast.
When Alexander discovered both sons had turned into aberrations, he could not bring himself to kill them. In the end he cast them out, while remaining hidden in the shadows and watching over them in secret.
Alexander Kervinas believed the world belonged to humans, not to the sons he had birthed. Thus he worked behind the scenes to manage the aftermath and keep everything under control.
To Chen Mo, the most valuable thing in the Underworld world was the "perfect blood" carried by that first immortal.
Vampirism and lycanthropy could grant immortality and great power, but their drawbacks were too obvious and the physical changes were unacceptable to Chen Mo — he did not want to become a monster. The pure "perfect blood" lacked those problems; it was the thing Chen Mo truly needed.
He had been searching for Alexander for a long time with no success. Partly because Chen Mo's caravans had only reached limited places and intelligence was incomplete, and partly because Alexander had hidden for centuries, quietly cleaning up the mess his two sons made, making him difficult to find.
Chen Mo knew that finding either of the two sons would bring him closer to finding Alexander — that was the main reason he kept Marcus around.
But Marcus was not useless otherwise.
Though Chen Mo himself did not need turning, his knights could all be transformed into vampires — and then the strength of the entire order would be greatly enhanced, making it far easier to deal with werewolves, secular powers, and even the hidden presence of Alexander Kervinas.
As for the vampires' fatal weakness to sunlight, Chen Mo already had plans.
After turning Andrew into a vampire first, Chen Mo experimented on him. As Chen Mo had suspected, Andrew developed a bat-like echolocation ability.
With deliberate training, Andrew mastered that ability easily. He no longer needed sight; with hearing alone he could sense the surrounding environment, in full three-dimensional detail — even more accurately and comprehensively than the eyes.
That proved Chen Mo's hypothesis and solved the biggest problem. Under Chen Mo's orders the secret workshop ran at full speed; the castle echoed day and night with pounding hammers and grinding gears as one exquisite, advanced suit of armor after another was manufactured.
Chen Mo redesigned full-body plate armor that covered even the eyes. Wearing his new armor, vampire knights could operate in daylight without harm. So long as the armor did not tear, the vampire inside would feel no damage from the sun.
Thus was born a vampire knight legion that feared not sunlight and whose strength was unmatched.