"Because of all you have endured for Christ our God, you have been given a royal crown, O First and Holy Martyr Stephen! You have put your persecutors to shame and have seen your Saviour enthroned at the right hand of the Father. Do not cease to intercede for the salvation of our souls.
The saint whose name leads all the rest who have sacrificed their lives for Jesus Christ is Stephen, the first martyr of Christendom because he would have been the last to deny him.
Stephen was one of the seven deacons of the original Church of Christ in Jerusalem, sharing his duties with six others - Philip, Prochoros, Nikanor, Timon, Parmenas, and Nicholas." --from Orthodox Saints, vol 4, by Fr George Poulos, Holy Cross Orthodox Press
The Bible records his death in the Book of Acts of the Apostles:
When they [Sanheidrin] heard these things, they were cut to the heart, and they gnashed on him with their teeth. But he, being full of the Holy Ghost, looked up stedfastly into heaven, and saw the glory of God, and Jesus standing on the right hand of God, And said, Behold, I see the heavens opened, and the Son of man standing on the right hand of God. Then they cried out with a loud voice, and stopped their ears, and ran upon him with one accord, And cast him out of the city, and stoned him: and the witnesses laid down their clothes at a young man's feet, whose name was Saul. And they stoned Stephen, calling upon God, and saying, Lord Jesus, receive my spirit. And he kneeled down, and cried with a loud voice, Lord, lay not this sin to their charge. And when he had said this, he fell asleep. -- Acts 7: 54-60