Wow, Superman is interesting idea. Would love to hear how that would ho.
And you are right, pop culture slowly turns into myth that feels historical. And it can also be inspired by history like Dracula. The vampire has very little to do with the original yet historicity only added oil to the flame so to speak and gave it more strength. Perhaps king Arthur or Merlin were pop culture figures of their time too. I play with idea that the same might have happened with Jesus. Not intending to offend anyone, but I find it interesting, because it is proven that myths and tales influence the real life way more than how real life influences myths.
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So for myself, currently I'm actively working with Sephiroth (FF7 Character) and Alucard. (Castlevaina)
Alucard has been with me for years now and helps me with getting into vampirism and its current. Sephiroth, he is of immerse willpower and discipline, which is something I truly need to develop myself. Also I like blades and Sephiroth gave me proper push to start practicing katana. I have training blade which is much safer than real sharp one would be, but weight is very similar and practice is just as real. I could consider those two my guides. I treasure their help.
For superman, we already have a pretty iconic sigil to focus on, multiple currents & versions of him to establish epithets, and a trademark "stance" if we wanted an asana. Writing an invocation wouldn't be too hard either if just focusing on solar aspects. The real question to me is why I would pick him over other already existing deities and figures that represent what I would want to cultivate in him? Helios, Surya, Archangel Michael, etc all seem to offer more in terms of established ritual to build from, not to mention divine names that seem to already carry a strong-enough power source to offer an easy "in" to their magical current.
For yourself, it seems like the associations and properties you want to cultivate in yourself from your characters are more multifacted than my plain-jane solar attributions, so it makes much more sense!
I would totally agree on the Arthur & Merlin point of being pop culture figures of their time, along with the myths of Hercules for the Greeks, or Arjuna for Indians, great generals for Chinese, etc. I've been reading more about voodoo recently and it seems like since many of their loas are built off of "heroic dead" that may have once lived historically, these form spiritual entities that are much more capable of understanding the human condition, and supporting their devotees in ways that make more transactional sense than an archetypical symbolic aggregate that many deities are.
I also agree with your point on Jesus and biblical myth, and I don't think this takes away from their influence! Personally, I place myth ABOVE historicity when it comes to magical current, as the imagination & mind seem to originate in a higher ontological sphere that places them closer to where identity exists as mythology and symbol, rather than objective, factual, lived dates and experiences. This allows us to experiment and grow metaphysical models, making our maps of consciousness more versatile, and hopefully if we're out of the armchair, our personalities & lived experienced more versatile!