Who was Stephen the martyr?

Stephen was called by the twelve apostles to be one of seven men set apart to help the 12 . . . specifically to care for the converted Greek widows.

He was likely a Jew (not a converted Gentile) because in Acts 7 he quotes the Old Testament at length (something young Jewish boys learned to do in school).  

Stephen was accused of blasphemy by false witnesses and put to death by stoning– the Jewish form of capital punishment for that crime (Leviticus 24:16).