Neanderthal

Neanderthals are a species, related to Humans, who existed in early human history. The Neanderthals were wiped out by the Humans, with the help of the Dæmons, who assisted the humans for unknown reasons. (DW: The Daemons)

Physically very like humans, they had jutting brow ridges, large noses and stooped postures. However, while stereotyped as brutish by later humans, Nimrod showed intelligence and spoke articulately.

The tribe which Nimrod originally belonged to herded mammoths during the summer for food. They considered the fang of the cave bear to be a sign of wisdom. The tribal elders "spoke with the voice of the Burning One". The actions of the Doctor implied that at some time in the past, the Doctor had encountered the Neanderthal species some time before. (DW: Ghost Light)

Nimrod referred to Light as "The Burning One", implying that his worshipped him. Or possibly they originally worshipped another deity or the Sun as the Burning One and when Light appeared, transferred their worship to him.