Does the honor fall on TES?
As you probably know, most fiction involves some manner of lore, even if it's as simple as COD zombie lore, (No, I'm not joking) or Super Mario lore. (Sadly, still not joking.) Although there are plenty of noble contestants, such as The Lord of the Rings or Dark Souls, I don't see the same brute information, let alone the staggering depth of topics such as CHIM or other metaphysics. (Believe it or not, TLR is actually set on our earth.)
Of course, it would be unfair not to mention TES' grandfather, the dull and generic D&D. I don't know a whole lot about this universe, and it obviously lacks in depth and originality, but complexity, I cannot judge.