A person who writes and does commentary is a commentator. A commentator is someone who passes his opinion about any certain a topic or area of expertise to the public. There are various types of commentators ranging from topic to topic. He/ she could be a professional or an amateur at the particular topic and yet make statement. Commentary is usually seen in sports or news organizations.
Commentators are usually asked to give their opinions about a particular decision, action or statement. This helps others who are watching the TV show or news channel or any sports match to understand what is happening at the place without having to go there personally. It could be done on radio and through TV especially on news channels and sports commentaries.
Commentators are mostly found only in the sports area or some new channels. They aren’t quite popular for any other genre other than that. Some commentators, who retire, find other roles in the entertainment industry itself.