Firebrand

firebrand \FYRE-brand\ noun
1 : a piece of burning wood
2 : one that creates unrest or strife (as in aggressively promoting a cause) : agitator

Example sentence:
John views himself as a relentless firebrand who stands up for his beliefs even when they are not popular.

Did you know?
The original firebrands were incendiary indeed; they were pieces of wood set burning at the fire, perhaps for use as a light or a weapon. English speakers started brandishing those literal firebrands as long ago as the 13th century. (Robinson Crusoe held one high as he rushed into a cave on his deserted island and saw "by the light of the firebrand... lying on the ground a monstrous, frightful old he-goat.") But the burning embers of the wooden firebrand quickly sparked figurative uses for the term, too. By the early 14th century, "firebrand" was also being used for one doomed to burn in hell, and by 1382, English writers were using it for anyone who kindled mischief or inflamed passions.