In Rome whose job was it to help protect the rights of the common people

The Tribunes of the Plebs were supposed to protect the rights of the common people. For the most part they did. Their doors were always supposed to be open, during the time in office, so people could come to them for help with legal problems. However by the end of the Republic, the Tribunes were also surrogates for the counsul or political group that helped him to get elected and he used his veto to further their interests regardless of its effect on the common people.