Dissident

Dissident:When people disagree with or criticize their government or a powerful organization they belong to.
Dissident is an adjective and a noun.

•  The noun is a person who disagrees with and criticizes their government, especially because it is undemocratic. disagree with or criticize their government or a powerful organization they belong to.

The adjective is to disagree with or criticize the government or a powerful organization.
I do not know any famous dissident though. Ok, bye!