R'hllor, alternatively known as the Lord of Light, is a deity widely worshiped on the continent of Essos. The Lord of Light has been described as a "fire god" and its clergy "fire priests", as His worship centers around fire and light.
He is also known as the Red God, the Heart of Fire, and the God of Flame and Shadow.
The faith of the Lord of Light is the majority religion in several of the Free Cities, and extends to Asshai in the distant east. Worship of the Lord of Light is almost unheard of in Westeros.
The religion of the Lord of Light is centered on belief in the existence of two deities, in the words of Melisandre: "A god of light and love and joy, and a god of darkness, evil, and fear, eternally at war." R'hllor is the god of fire, which provides light, heat, and life, and struggles against darkness, cold, and death, represented by an opposing deity, the Great Other.
Due to the dualistic worldview of this religion, its more fanatical followers believe the Lord of Light is the "one true god", and all other gods from other religions - The Old Gods of the Forest, the Faith of the Seven, the Drowned God, etc. - are demons and false idols that must be cast down and burned.
Members are called Red Priests and Priestesses with notable members such as Melisandre,Kinvara and Thoros Of Myr who all display what could be classified as magic or Force like abilities