a person who fights against the government of their country

a person who opposes somebody in authority over them within an organization, a political party, etc.

A number of Tory rebels are planning to vote against the government.

The Education Secretary has made further concessions to the back-bench rebels.

a person who does not like to obey rules or who does not follow generally accepted standards of behaviour, dress, etc.

I've always been the rebel of the family.

He was a rebel in his teens but he’s a respectable citizen these days.

to fight against or refuse to obey an authority, for example a government, a system, your parents, etc.

LEARNit Dictionary