Judge Mathis' first name is Greg. He has risen to fame as he was originally the wrong side of the law and spent time in prison, but has since changed as it now of the other side of the law as a Judge. Now he is watched by millions on his own television show.
'Nick' is another word for Prison [UK] Jail is a word for spending more than a year in police custody. Prison is a word for spending less than a year in police custody. So jail could be another word for prison, although it is not exactly prison.