A person who causes trouble or inspires change through inflammatory speech and actions, or historically, a burning stick or torch.
Compound of 'fire' and 'brand' (a burning piece of wood). The metaphorical meaning evolved because a firebrand, like a controversial person, spreads and ignites trouble.
Political firebrands like Martin Luther King Jr. and Malcolm X were called this because, like literal firebrands that spread fire, their words and actions spread ideas that changed the world—and made the powerful deeply uncomfortable.
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