Stephen (d. A.D. 36) was the first Christian martyr (after Jesus). As recounted in the Acts of the Apostles chapter 7, Stephen was stoned to death for providing witness in public and standing up against pressure to recant. His feast day is December 26.
Stephen was a foreign-born Jew fluent in Greek, a Hellenist.
He was a powerful evangelist who converted many Jewish priests, resulting in a backlash against him by the Sanhedrin, which was the equivalent of the supreme court of rabbis in Jerusalem. He was charged with an extremely vague "crime" of talking against “this holy place and the law.” His defense on his own behalf is what caused him to be executed. Stephen was more critical of the temples (and sacrifices) in Jerusalem than other early Christians, including Paul, were. Paul, then named Saul before his own conversion to Christianity, was in approval of the execution of Stephen.
The execution of Stephen within years -- perhaps merely months -- after the Resurrection of Christ means that the Epistle to the Hebrews was written in that brief period, because it mentions how disciples had not shed blood yet.