What was a noble citizen in ancient Rome called, who was the defender of their client in court?

My adult son has been teaching me so many facts of the Romans. He is so intelligent and I love learning history.

a noble was called a patrician, patricianus, related to father. a commoner, not necessarily poor, was called a plebian. a middle class was called equitanus, a knight, horse owner. In the days of the Roman empire the patron was anyone who supplied bread and succour to his followers. Often wealthy plebian merchants.