noun
vanguard; forefront; leading figure
Refers to a person or group at the forefront of a movement, campaign, or cause, often with a sense of being radical or aggressive. Common in political and social contexts.
He is known as a leading figure in the reform movement.
その議員は党内の急先鋒で、しばしば過激な発言をする。
That lawmaker is a radical vanguard within the party and often makes extreme statements.