The idea that major religious figures are ambassadors from outer space goes back at least to…

The idea that major religious figures are ambassadors from outer space goes back at least to Theosophy, with its idea of “secret chiefs”; Theosophy was extremely influential, particularly on the ideas of other syncretic religious groups, so it’s not a surprise that the Aetherius society has adopted this idea (just as the Raelians have). It’s also not surprising that it made its way into pop culture, since Theosophy was basically the Spiritualism of the 1920s: a minor religion with very influential followers that captured the zeitgeist & thus had an overwhelming effect on popular discourse.