The author of Jude identifies himself simply as Jude, brother of James and servant of Jesus Christ. There are eight New Testament persons with the name Jude (Greek, Judas, or Hebrew, Judah), but the most likely is Jude the brother of Jesus. Of the various persons named Jude in the New Testament, only the brother of Jesus and James would be well known enough to identify himself so simply.
If Jude was the brother of Jesus, why does he not say so in his letter? Why use the title “servant of Jesus?” The fact that Jude and the other brothers of Jesus were unbelievers until after the resurrection, the title “servant of Jesus” can be seen as a humble acknowledgment of Jesus’ Lordship.
Objections to this identification center on the language of the book, which seems too Hellenistic for an author who grew up in Galilee. The vocabulary is obscure and is full of rare words, including thirteen words not found elsewhere in the New Testament. This objection does not carry much weight since the author is familiar with at least two popular apocryphal texts, indicating some degree of education and sophistication.
We know virtually nothing about Jude, the brother of Jesus, in the New Testament. Jude is listed in Matt 13:55 and Mark 6:3 simply as a brother of Jesus. He likely was not a believer during the ministry of Jesus, (Mark 3:21, 31). He would have become a believer after the resurrection (Acts 1:14), but we know nothing of his conversion, whether he was a witness to the resurrection, etc. The “brothers of Jesus” are mentioned in 1 Cor 9:5 as having taken believing wives, although it is not clear whether this is literal brothers or not.
According to tradition reported by Julian Africanus, the brothers of Jesus were involved in missionary activity. Eusebius. (Hist. Eccl. 1.7.14) says that the family of Jesus evangelized Palestine. In another section (Hist. Eccl., 3.19.1 – 20.8) the grandsons of Jude are arrested during the reign of Domitian. Since they are in the line of David, they are potential messianic pretenders. Domitian allegedly interview them but they claimed to be farmers – as evidenced by their calloused hands! This story has always struck me as legendary, since I cannot imagine Domitian rounding up potential Jewish rebels from Palestine.
It is somewhat intriguing that a brother of Jesus should write a book which is so much dependent on the Hebrew Bible. Perhaps, like his brother James, Jude was well trained in the Hebrew Bible and able to use the scripture to argue against a false teaching within Jewish Christian communities.
It is not critical that the Jude of the letter of Jude is a brother of Jesus. This tradition helps explain how a letter like this was accepted as canonical, but it is not required by the text since it does not state that the writer is the brother of Jesus.