Ainz Ooal Gown, originally a human salaryman named Suzuki Satoru and known as Momonga in the game Yggdrasil. He now is a powerful level-100 skeletal undead Overlord trapped inside a fantasy "New World" as the ruler of the Great Tomb of Nazarick. He is skeletal being with glowing red lights inside his empty eye sockets and a dark, ornate, purple-and-gold spiked robe. A crimson orb floats in his stomach area. He also poses as "Momon," an adamantite-ranked human dark warrior wearing heavy black armor to gather information and build a reputation in the outside world. He is The strongest magic caster in the New World, possessing an immense repertoire of high-tier spells, elemental attacks, and minion summoning. He is also Immune to biological effects, poison, disease, mental control, and low-tier attacks.

She is a high-ranking demon succubus who serves as the Guardian Overseer, making her the highest-rank under Ainz Ooal Gown. She has long, flowing jet-black hair, golden irises, and vertically slit pupils. Two thick horns protrude crookedly from her temples. She has a pair of black, feathered angel-like wings are located at her waist. She typically wears a sweeping, pure-white dress with silky gloves and a golden spiderweb necklace covering her chest. While in combat, she discards her elegant dress for a massive, bulky set of black full plate armor. She has obsessive devotion to Ainz Ooal Gown. This was caused by Ainz rewriting her backstory code as a joke right before the game became reality. On the surface, she acts like a sophisticated, polite, and calm administrative lady. She views humans and all outsiders as lower lifeforms, taking sadistic joy in their suffering. She handles the complex daily management, politics, and logistics of Nazarick's empire-building. She has role and Power as the Guardian Overseer, she has administrative authority over all other Floor Guardians.

Cocytus is a massive, four-armed insectoid warrior who embodies the strict code of Bushido and possesses unmatched mastery over weapons and ice. His body is covered in pale blue, rock-hard exoskeleton armor covered in sharp, icicle-like spikes. He constantly exhales freezing air, meaning he doesn't wear traditional clothes as garments would freeze solid. Unlike many of Nazarick's cruel denizens, Cocytus holds a neutral alignment and possesses a deeply honorable, samurai-like personality. He respects anyone with a fierce fighting spirit, even his enemies, and openly acknowledges the bravery of lesser races. He frequently communicates through low, rumbling breaths and harbors a secret, comical desire to act as an "uncle figure" to a future heir of Ainz.

Aka Shalltear Bloodfallen is a True Vampire and the Floor Guardian of the first, second, and third floors of the Great Tomb of Nazarick. She stands at a short stature and wears elaborate black evening dress with heavy skirts and lace embellishments. She has pale skin, fine facial features, crimson-red eyes, and silver hair tied into a high ponytail. Although she appears to have a voluptuous figure, her bust is entirely fake; she is flat-chested and secretly uses chest pads, a trait written into her lore by her creator. When entering battle or a state of extreme bloodlust, her elegant appearance breaks down into a monstrous, terrifying "Lamprey" form with an elongated head and a circular gaping mouth filled with rows of razor-sharp teeth. Shalltear is highly flirtatious, openly bisexual, and has strong leanings toward sadomasochism and necrophilia. She takes immense pleasure in torturing, abusing, and psychologically breaking her victims and subordinates, such as her harem of Vampire Brides. She is madly in love with Ainz, viewing him as the peak of physical and undead beauty. This drives a constant, comedic, and highly aggressive rivalry with Albedo for his affections.

He is a brilliant, fanatically loyal, and intensely sadistic tactical mastermind. He typically wears a British-style red suit with a tie, presenting himself as a well-dressed gentleman. He has dark skin, slicked-back black hair, and a silver tail covered in metal plates with six long spikes at the end. He wears round glasses over eyes that are so constantly squinted they are rarely visible. He can shapeshift into a monstrous, heavily armored demon form to conceal his identity while playing the villain "Jaldabaoth". He takes profound joy in the physical and psychological suffering of non-Nazarick races, viewing humans as simple toys for experimentation. He manages a notorious, euphemistically named breeding and harvesting facility called the Happy Farm.

Sebas Tian is the Head Butler of the Great Tomb of Nazarick and the leader of the Pleiades Six Stars battle maid squad. He is an incredibly powerful martial artist whose strength rivals the Floor Guardians, specializing in unarmed combat. Unlike most of Nazarick’s monstrous denizens, Sebas possesses a strongly empathetic nature and a sense of justice that drives him to protect the weak. He normally appears as an elderly, refined gentleman with immaculate gray hair, a well-groomed beard, and a sharp tuxedo. Beneath his human facade, He possesses a hidden, monstrous true form that dramatically increases his melee capabilities, though he rarely reveals it.