The god behind the extremely controversial, fire-based belief system in Game of Thrones is variously known as the Lord of Light, the Red God, and R’hllor. He attracts followers from all walks of life. Game of Thrones fans are familiar with multiple Red Priests and Priestesses, including Thoros of Myr and Melisandre, and they are as diverse as they are powerful.
The religion of the Lord of Light—colloquially known among book-readers as "R’hllorism"—has already made a massive impact on the story. Without the Lord of Light, several dead characters would have remained dead instead of coming back to life. We also wouldn't have access to several important visions of the future. Most importantly, more than a few world-changing battles would have gone much differently. On the other hand, faith in R’hllorism also directly led to a small, innocent child being burned alive. It’s easy to see why the religion is controversial. So let's examine the history and lore of R'hllor and find out if it's worth converting.
The main practitioners of the religion of the Lord of Light are Red Priests and Priestesses, who are most often trained from a young age in red temples. Sometimes, red temples will buy slave children and raise them as priests. Families have also been known to voluntarily give up their unwanted children.
The religion—referred to in A Song of Ice and Fire fandom as R’hllorism—also has a warrior class known as the Fiery Hand. Both Red Priests and Fiery Hand warriors are easily recognizable by their crimson outfits, and they’re both a common sight in Essos. In Westeros, however, the religion has only just started to gain traction.
The lore of R’hllor mostly revolves around the legend of Azor Ahai, the champion of the Lord of Light. During a period of darkness in the world, most likely the Long Night, R’hllor empowered Azor Ahai to rise up and defeat the forces of evil.
Azor Ahai fought against the darkness with Lightbringer, a powerful sword with a convoluted tempering process. Azor Ahai had to try and forge the sword three times, plunging the molten blade through water, a lion's heart, and his wife, in that order.
Likely, this is why followers of the Red God believe so strongly in the power of sacrifice—unfortunately for Shireen Baratheon. True believers also claim that, one day, Azor Ahai will be reborn to lead them against the forces of darkness once again.
R’hllorism is described as a “dualistic and Manichean” view of the world. The being R’hllor represents light, fire, and life. He has an antithesis called the Great Other who represents darkness, ice, and death. The two are locked in an eternal battle for the fate of the world. Followers of the Lord of Light believe they need to help him win that battle.
Little else is known about the Great Other, and his true name is never spoken. If there truly is a Great Other, it would make sense for him to be connected to the Night King and the White Walkers, known as the Others in the books. Melisandre, the most notable Red Priestess in the story, believes the White Walkers directly serve the Great Other.
R’hllor's great power been clearly demonstrated on several occasions in both Game of Thrones and A Song of Ice and Fire; however, it’s still unclear whether or not the deity himself actually exists. According to George R. R. Martin, that’s one mystery that will remain unsolved. In an interview, he said:
“Well, the readers are certainly free to wonder about the validity of these religions, the truth of these religions, and the teachings of these religions. I'm a little leery of the word ‘true’—whether any of these religions are more true than others. I mean, look at the analogue of our real world. We have many religions too. Are some of them more true than others? I don't think any gods are likely to be showing up in Westeros, any more than they already do. We're not going to have one appearing, deus ex machina, to affect the outcomes of things, no matter how hard anyone prays. So the relation between the religions and the various magics that some people have here is something that the reader can try to puzzle out.”