The author has been identified in the past with both "Judas, the brother of James" the Less (Jude 1:1), called also Lebbaeus (Matthew 10:3) and Thaddaeus (Mark 3:18), as well as Jude, the brother of Jesus Christ. However, the ascription of this epistle to either historical figure was early questioned, and doubts regarding it were revived at the time of the Reformation. Scholarly consensus afterwards moved back to the belief that this was the writing of either the apostle or relative of Jesus, but since at least the beginning of the 20th century this has been believed to be the anonymous work composed as late as the first quarter of the 2nd century. Based on the nature of the allusions to the Old Testament, citations of noncanonical works like the Book of Enoch, and the use of the authority of Jude, current belief places its composition in Palestine.
The epistle is addressed to Christians in general (ver. 1), and its design is to put them on their guard against the misleading efforts of a certain class of errorists to which they were exposed. The style of the epistle is that of an "impassioned invective, in the impetuous whirlwind of which the writer is hurried along, collecting example after example of divine vengeance on the ungodly; heaping epithet upon epithet, and piling image upon image, and, as it were, labouring for words and images strong enough to depict the polluted character of the licentious apostates against whom he is warning the Church; returning again and again to the subject, as though all language was insufficient to give an adequate idea of their profligacy, and to express his burning hatred of their perversion of the doctrines of the gospel." The doxology with which the epistle concludes is regarded as the finest in the New Testament.
The striking resemblance this epistle bears to 2 Peter suggests that the author of one had seen the epistle of the other. Because this epistle is much shorter than that creditted to Peter, and various stylistic details, the scholarly consensus is that this work was the source for the similar passages of the other.
The above includes text from Easton Bible Dicionary, Third Edition of 1897
The true identity of Jude is clouded by opinions within the Christian community: