"Herod the king" was Herod Agrippa I whom the Roman emperor Gaius appointed king over Palestine in A.D37. He ruled Judea for three years, A.D41-44 [1] (cf. Acts 12:23), and moved his headquarters to Jerusalem. Herod Agrippa I had Jewish blood in his veins and consistently sought to maintain favor with and the support of the Jews over whom he ruled, which he did effectively. [2] As the Christian Jews became increasingly offensive to their racial brethren (cf. Acts 11:18), Herod took advantage of an opportunity to please his subjects by mistreating some believers and by executing the Apostle James , the brother of John (cf. Matthew 20:23). This is the only apostle"s death that the New Testament recorded. James was the second Christian martyr whom Luke identified (cf. Acts 7:54-60). Persecution of the Christians now swung from religious to include political motivation. [source][source][source]
It is noteworthy that the Christians evidently did not seek to perpetuate the apostalate by selecting a replacement for James as they had for Judas (ch1). They probably believed that God would reestablish The Twelve in the resurrestion. [3][source]
Roman Emperors in New Testament TimesEmperorImportant EventsBible Books WrittenAugustus(31 B.C-A.D15)Ordered the census that took Joseph and Mary to Bethlehem ( Luke 2:1).Tiberius(A.D15-35)Jesus" earthly ministry conducted during his reign ( Luke 3:1; Luke 20:22; Luke 20:25; Luke 23:2; John 19:12; John 19:15).Gaius(A.D35-41)Appointed Herod Agrippa I king over Palestine ( Acts 12:1).Matthew (A.D40-70)Claudius(A.D41-54)Extensive famines ( Acts 11:28).Expelled the Jews, including Priscilla and Aquilla, from Rome ( Acts 18:2).James (A.D45-48)Galatians (A.D49)1 & 2Thess. (A.D51)Nero(A.D54-68)Paul appealed for trial before him ( Acts 25:11).Favored Christianity early in his reign, but when Rome burned in64 A.D. he blamed the Christians and from then on persecuted them.Had Paul and Peter executed (according to early Christian tradition).1 & 2Cor. (A.D56)Romans (A.D57)Luke (A.D. 57-59)Prison Epistles (A.D60-62)Acts (A.D. 60-62)1Tim. (A.D. 62-66)Titus (A.D. 62-66)Mark (A.D. 63-70)1Pet. (A.D. 64)2Tim. (A.D. 67)2Pet. (A.D. 67-68)Jude (A.D67-80)Galba(A.D68-69)Hebrews (A.D68-69)Otho(A.D69)Vitellius(A.D69)Vespasian(A.D69-79)Crushed the Jewish revolt against Rome (A.D66-70).His Song of Solomon ,, Titus , destroyed Jerusalem (A.D70).Titus(A.D75-81)Domition(A.D81-96)John (A.D85-95)1 , 2 & 3John (A.D90-95)Revelation (A.D95-96)Nerva(A.D96-98)[source]