What fictional characters outside the DCU would be considered worthy of a Green Lantern power ring? Or other DCU characters, so long as they’re not ordinarily associated with the Corps. (I think it’s canon that Superman was actually Abin Sur’s first choice for his successor, but it was decided that he either wasn’t a representative Terran (not being one in the first place) or that he was already powerful enough on his own.
My first nomination for non-DCU character: Aragorn son of Arathorn. Book version, of course, not movie, and before he became king of the reunited kingdom; I rather think the Guardians would automatically disqualify any monarch. Fearless? Check. Honorable? Check. Iron will-power? Double-check. The only problem would be that he’d automatically be distrustful of magic rings.