The simplest explanation is that Elidibus, in trying to counter the Warrior of Darkness (us), uses a trope that has long been part of Norvrandt legend to pattern himself as the Warrior of Light.

I doubt that the book we see, with its artist's drawing of the fabled hero, is to be taken as a literal depiction of the original Warrior of Light on the First.

I point out that everyone who has read Sherlock Holmes books and stories has an idea of what he looks like. Actors who have portrayed him in movies and video games rely on artists' drawings, in particular those of Sidney Paget. Did Sherlock Holmes actually look the way he is was drawn? Without a photograph (which Conan Doyle does not provide), we will never know ...

[The last paragraph only slightly tongue-in-cheek, with apologies to Sherlockian's everywhere]