Jude identifies himself
The opening line gives the author’s name: Jude. He describes himself first as a servant of Jesus Christ, then as the brother of James (Jude 1:1). That is the most direct answer Scripture gives.
Jude could have led with a family connection, but he did not. His chosen identity is someone who belongs to Jesus and serves him. For Jude, devotion to Christ mattered more than status.
Jude, the servant of Jesus Christ, and brother of James, to them that are sanctified by God the Father, and preserved in Jesus Christ, and called:
Was Jude related to Jesus?
Many readers connect this Jude with Judas, the brother of James, Joses, Simon, and Jesus, named in Matthew 13:55 and Mark 6:3. On that reading, Jude was part of Jesus’ earthly family and the same James was likely James, a recognised leader in the Jerusalem church (Galatians 1:19).
Christians do differ over how to understand the Gospel references to Jesus’ brothers. Many Protestants take them as children of Mary and Joseph. Catholic and Orthodox Christians have traditionally understood them as close relatives or children from Joseph’s earlier family. Whatever view someone takes, Jude’s letter plainly presents its writer as James’s brother and Jesus’ servant.
Not Judas Iscariot
Jude is the English form of Judas, a common name in the first century. He is not Judas Iscariot, the disciple who betrayed Jesus. The author distinguishes himself by naming James as his brother, and he speaks of the apostles as people whose teaching his readers should remember (Jude 1:17).
He also does not claim to be one of the Twelve. Instead, he points his readers back to the apostolic message already given to the church. It is a humble introduction, but it carries conviction.
But, beloved, remember ye the words which were spoken before of the apostles of our Lord Jesus Christ;
Why his authorship matters
Jude wrote a short, urgent letter calling believers to contend for the faith they had received (Jude 1:3). He explains that ungodly people had entered among them and were twisting God’s grace into permission for sinful living (Jude 1:4).
So the best answer is that Jude was Jude, or Judas, the brother of James, traditionally identified by many as a close relative of Jesus. His letter does not rest its authority on family ties, though. It calls readers to remain faithful to Jesus Christ and the truth handed down through his apostles.
Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort you that ye should earnestly contend for the faith which was once delivered unto the saints.