What's a word for somebody you’ve never met?

I know what you mean, I think. It's elusive, though.

Paragon?

While he is a stranger, he is also a mentor.

I would use either role model or mentor.

Could you just go for the emotional component, and say that that man is an inspiration?

For my ears it's a broader word that better grabs the 'influence in some way' aspect of it all esp if you pair it with the "I've not met him" opening. For example:

I'm trying to think of a word for somebody I've never met, but who has influenced me.

Like Steve Jobs, I've never met him, but he continues to teach me.

He's like an invisible hand to me. An unmet teacher. An inspiration!

(gratuitous exclamation mark added for effect)

I understand the feeling and reasons that prompted you to ask. There is a vacancy in vocabulary for this particular fandom. I recoil at the thought of those people that made a point to make a comment on clearly something they are mentally unequipped to answer, yet that is not their fault.

You could stretch to refer to Latin if nothing else is quite one-the-head.

Persona Grata, perhaps.

At a long stretch in this 21st Century a reinvention of the word Amicus may have viability for such description.

I often find the best part of writing in our English language is the puzzles one must solve in order to correctly arrive at a point, emotion or purpose. Try to have fun using multiple words when one word is not enough, often one word may seem to be perfect to the speaker but quite often the audience needs more information.

My Kindred Friend.

oracle

Perhaps not an exact match or obvious choice for this question but neither an exact match, nor an obvious choice sprang to mind.