This monster is a 4e beastie that I have converted to use in my PUG game. I particularly love it because it uses a number of 4e mechanics that I actually really liked. In that edition, these monsters were "Soldiers" - creatures designed to tank the party, and to free up the squishier monsters so they could do their thing. I have tried to keep this role in their 5e incarnation, designing them to serve as effective front line fighters that have a few surprises up their flaming sleeves.
Flamespikers were a common sight during the Guild Wars of the early 2nd Age, being summoned en masse to fight for this mage or that order. They are also commonly called by mages fighting in 2nd Age Upper Malgoroth's internecine and endless wars. In later ages, they tended to be seen in those places where one would encounter other elementals of fire, though after the Sundering, many of these monsters were dragged into certain realms within the Physical Plane, and remained there afterwards.