One aspect of deities seems to be thought-forms. That is not to say that deities are merely thought-forms, but that part of the way we interact with them seems to be through our internal image of what they are like. The more people carry an internal image of that deity around in their heads, the easier it is to visualise them.
This thought occurred to me because I wondered why it was so easy to visualise Jesus. Then I tried it with other well-known images, such as Robin Hood, Kuan Yin, Gandalf, Che Guevara, Superman, and even the man with the thistledown hair from the novel Jonathan Strange and Mr Norrell. So it is not because Jesus is a powerful deity that he is so easy to visualise, but because his image is so ubiquitous and has a number of consistent features (beard, robe, long face, big eyes, etc).
Odin has a number of consistent features about his image (one eye, pointy hat, staff) but his image is less widely-known, so it is less readily available from the collective unconscious (or wherever it is that these images are “stored”).
Doctor Who has changed his appearance very frequently, so despite being widely known as a character, his imagery is not consistent, so he is harder to visualise.
This is presumably why some magical practitioners choose to work with figures from popular culture: because their imagery is widely known, consistent, and readily available, so they make a powerful thought-form.
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