The Wrathborn are the Red-aligned Triumvirate cult. They believe that only emotions, especially Wrath, lead to divinity.
There are three races in the Triumvirate cult: Flames, Wrathborn and Dwarfs, where the flames have the highest and the dwarfs have the lowest social state.
Of course, the most numerous race are the Wrathborn themselves. These humanoid and sentient beings founded the cult around Wrath and its physical manifestation Fire. Today, most of them serve the purpose to protect the cult and the dwarfs or to serve the honored flames. Especially, they oversee a dwarf's transformation to a flame and make the flames permanent in a sacred ritual.
These also sentient beings are mainly miners and smiths, but serve a much more important purpose, too: Some day, every dwarf ignites himself and bursts into flames. Then, as is described above, the resulting flame is "made permanent". They are mostly treated similar to children by the flames and the Wrathborn.
Flames are perceived as the manifestation of Wrath itself and generally emotions by the cult and are the most honored members of it, so most of the government are flames. In the most cases, a flame is indeed an ignited dwarf, but someties natural fire is stabilized by the Wrathborn, too.