A group of people who rule the country (noun)

A group of people who rule a country is typically referred to as a "government." When referring to the individuals specifically, you might be talking about the "ruling class" or the "political elite." If you need a more specific term, for example, the small group at the top of the political hierarchy, they might be called the "cabinet" or the "executive." If it is an informal or pejorative term you are looking for, such terms as "regime" or "junta" could apply, particularly in contexts where the government is not democratically elected.