What is a word for the thing or idea that something personifies?

Although it is often used to refer to mechanical contrivances, I would sometimes use prototype in this sort of circumstance.

prototype 1 : an original model on which something is patterned : ARCHETYPE 2 : an individual that exhibits the essential features of a later type

Merriam Webster

Otherwise:

Archetype = typical example of something, or the original model of something from which others are copied:

Cambridge

These words do not specifically personify, although they may do so as in the following example.

”The fact that Hitler is (rightfully) our universal archetype of monstrously inhuman dictator rather than Stalin is mostly because of the not insignificant detail that we were allied with the latter in the world’s biggest war.”

Wrath-bearing Tree

I would call them vehicle and tenor, respectively— the whole thing being a metaphor.

Tenor

The word, phrase, or subject with which the vehicle of a metaphor is identified, as life in “Life's but a walking shadow” (Shakespeare).

[American Heritage Dictionary]

I doubt if this is an example of personification, though. That is when you liken a non-living entity to a living one.