A word for a person on the very extremes of a spectrum

In a novel I am reading, there are many characters that embody various ideological extremes that end up informing the protagonist's viewpoint. His sister is very politically progressive, his friend incredibly nationalist and conservative. But these spectrums are not just political - one man he meets is incredibly nihilistic, and another a complete hedonist. I am trying to fill in the following sentence:

[The protagonist] is able to incorporate lessons from each of the ideological _______ that he meets, with each informing a facet of his ethical beliefs.

Is there any word that can fill in the blank? I thought of radicals or stereotypes, but the former (to me) has a violent connotation, while the latter implies that such a character is common, which is not the case. I am not trying to imply that these people are completely "out-there", but rather that they completely embody each of their respective main qualities.

Is there a good word for someone who falls on an extreme end of an ideological spectrum?

Solution 1:

archetype

Being that the term is for characters and since the purpose of those characters is to typify an extreme or imitate an extremist of that type, you might use the term "archetype."

In Greek mythology, Narcissus is an archetype, an archetype for extreme self-absorption and fixation on oneself such that the word in English for that, "narcissism," is derived from his name. So, if these characters are being used in the same way, to typify a certain personality or ideology, which is often done through extremism like with Narcissus, then "archetype" is the word you're looking for.