That would be James the son of Zebedee.
He was one of Jesus’ core disciples. He—together with Peter and his own brother John—were the three privileged to witness the Transfiguration, for example (Mark 9:2), and this was not the only time Jesus singled out the these core disciples (cf. Mark 5:37, 13:3, 14:32-33).
When the names of the Twelve apostles are given, they’re always given in three blocks of four names (Matt. 10:1-4, Mark 3:13-19, Luke 6:12-16, Acts 1:13). This James, together with Andrew, Peter, and John, is always listed in the first block of names.
He was also the first of the apostles who was singled out for martyrdom.
The King Who Did the Deed
The Herod in question is Herod Agrippa I. If you've ever seen the BBC miniseries I, Claudius, he is the Herod that is featured in it.
In real life, Herod Agrippa was a grandson of Herod the Great. He was a flamboyant character who spent time in Rome and was a friend of both the emperors Caligula and Claudius.
Caligula made him tetrarch of Galilee and Perea, and after Caligula was assassinated by his own guard, in January of A.D. 41, Agrippa helped Claudius through the delicate transition period that followed.
In gratitude, Claudius named Agrippa as "King of the Jews" and enlarged his territories to include Judea and Samaria.
Herod vs. the Church
Luke tells us:
About that time Herod the king laid violent hands upon some who belonged to the church. He killed James the brother of John with the sword [Acts 12:1-2].
This is the first martyrdom of an apostle. Herod meant to do more than kill James, though. Luke reports:
And when he saw that [James's execution] pleased the Jews, he proceeded to arrest Peter also. This was during the days of Unleavened Bread.
And when he had seized him, he put him in prison, and delivered him to four squads of soldiers to guard him, intending after the Passover to bring him out to the people.
So Peter was kept in prison; but earnest prayer for him was made to God by the church [Acts 12:3-5].
God miraculously delivered Peter from prison, however, which leads to a couple of highly comic scenes.
The first is when God sends an angel to release Peter from prison, and the angel tells Peter to get up, get dressed, put on his mantle, and follow him. Peter does so, but he thinks he is seeing a vision. They then walk past the guards, the iron gate of the prison opens by itself, and the angel leads Peter out onto the street and then leaves him.
Suddenly, standing on the street outside the prison, Peter realizes that this isn't a vision! It's real!
Peter then hurries to the house of John Mark's mother, where the faithful are holding a prayer service.
And when he knocked at the door of the gateway, a maid named Rhoda came to answer.
Recognizing Peter’s voice, in her joy she did not open the gate but ran in and told that Peter was standing at the gate.
They said to her, “You are mad.” But she insisted that it was so. They said, “It is his angel!”
But Peter continued knocking; and when they opened, they saw him and were amazed.
But motioning to them with his hand to be silent, he described to them how the Lord had brought him out of the prison. And he said, “Tell this to James and to the brethren.” Then he departed and went to another place [Acts 12:13-17].
Acts does not told where that "other place" was, but there are indications that Peter ended up in Rome, in the second year of Claudius (A.D. 42).
If so, the martyrdom of James would have occurred in the spring, just before Passover, of either A.D. 41 (when Herod became king) or A.D. 42 (assuming Peter arrived in Rome late in that year).
Peter's departure from Jerusalem led to the rise of another James--known as James the Just or James the "brother" of the Lord--who is referred to in Peter's parting instructions (above) and who became an important leader in the Jerusalem church.
Herod Meets His End
Herod's reign did not last long. He died in either late A.D. 43 or in A.D. 44.
Then he went down from Judea to Caesarea, and remained there.
Now Herod was angry with the people of Tyre and Sidon; and they came to him in a body, and having persuaded Blastus, the king’s chamberlain, they asked for peace, because their country depended on the king’s country for food.
On an appointed day Herod put on his royal robes, took his seat upon the throne, and made an oration to them.
And the people shouted, “The voice of a god, and not of man!”
Immediately an angel of the Lord smote him, because he did not give God the glory; and he was eaten by worms and died [Acts 12:19-23].
This event is also recorded, with some variations in detail, by the Jewish historian Josephus, providing independent confirmation of the basic biblical account.
Learning Our Story
The record provided in the book of Acts is part of our story as Christians.
It's helpful to us to understand that story better. The more we know about it, the closer we grow to our Christian heritage, and that can help us grow closer to God.
If you'd like to learn more about our Christian heritage, you should check out my book, The Fathers Know Best, which deals with the Church Fathers, who lived in the age that connects the world of the Bible to the later ages of Christian history.