Transcendent Pig
This most unusual creature -- if he is a creature -- is, in both nature and provenance, one of the most enigmatic in the entire field of errantry.
The first references to him on Earth occur in a rare few Chinese documents of the early X dynasty, where he is referred to as 卓越的豬 (the word "transcendent" can also be rendered as "remarkable").
...and even the Powers that Be are notably silent on the subject. It's said that none of them can remember having created the Pig (which casts the obvious uncertainty over the word "creature" as applied to him). He seems -- so the Manual says -- to have always been here, or been around.
...As might be expected of any being with such a peculiar, extensive, and clouded history, the Pig goes by many names and bears a host of epithets. He has been called "the Insoluble Enigma", ... But his name is a point on which there's some disagreement. Though wizards who meet him are frequently introduced to him as "Chao", it's not certain whether this is his personal name, or just another epithet: "chao" is simply a Chinese word for "pig".