Shalltear strongest Guardian

Shalltear Bloodfallen.
She was the strongest Guardian of the Great Underground Tomb of Nazarick.
Not even Albedo — no, nobody among the other level one hundred NPCs was capable of facing her.
[...]
Ainz was fully aware of that reason as well.
It was because Shalltear Bloodfallen was the nemesis of Ainz Ooal Gown. Ainz role-played an undead magician, and his character build focused on necromancer-type classes.
In other words, his character had been built for entertainment.
Shalltear, on the other hand, had been made with an optimized build. In addition, Shalltear’s divine magic caster classes could use many spells which were very effective on the undead, and she was adept at melee combat.

- Overlord; Vol 3; Chapter 4