noun

a person who opposes official policy, especially that of an authoritarian state.

a dissident who had been jailed by a military regime

dissenter,objector,protester,disputant,freethinker,nonconformist,independent thinker,rebel,revolutionary,recusant,renegade,subversive,agitator,insurgent,insurrectionist,insurrectionary,disruptor,mutineer,refusenik