WARNING: The following contains spoilers for One Piece by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English via Manga Plus and Viz Media.
Throughout the last few chapters of One Piece, hints have been dropped about the people who lived above the Red Line before Marijoa -- the seat of the World Government-- was built where their civilization once stood. Not only is it all but confirmed that King is a member of this race, but Queen also dropped a possible name for this group: the Lunarians. Given how much history has been revealed in the past few chapters, it's also possible that this race of people may have connections to the legend of the Sun God, Nika.
Thanks to Marco and his memories of Whitebeard, we know that the island where Marijoa now stands was once known as "the Land of the Gods." This implies that the people there were held in high regard and were capable of things that were thought impossible. One of the other legends we've learned about is that, among enslaved prisoners, there were stories of a savior who would come to free them. This savior was Nika.
When we first learn of the legend, Who's-Who asks Jimbei if it's true, but he doesn't give a definitive answer. It's entirely possible that Nika was indeed real, and that he was Lunarian. If they were seen as Gods, then Nika could very well be one of them, as he is called "the Sun God." It's been said that the people above the Red Line could manipulate fire, so this would definitely fit into the motif for a sun god. We know that King is capable of controlling fire to a much high degree than Sanji, and it's almost impossible to do so without the aid of a Devil Fruit. If Nika were to mingle among the other races and even help those who were enslaved, then his abilities would definitely raise him to deific status.
Who the Lunarians were and what they were completely capable of is still a mystery, but what we do know is enough for us to speculate on the connections. We know King controls fire and is from a race thought to be extinct. This race of people lived above the Red Line in a place called "the Land of the Gods." Nika is the Sun God and the savior of the enslaved. It's clear that there's something there, we just need more hints and clues to clear up the haze of what that something is. Hopefully, Oda will give us more to go on soon.