The beloved books of 1st, 2nd, & 3rd John were written by the Apostle John, who was one of the original 12 disciples. The authorship is not indicated in the text of the letters such as is found in the Pauline letters. Nevertheless, external evidence for the authorship of these three epistles by John is strong and without significant controversy.
The Apostle John wrote five New Testament books: the Gospel of John, 1st, 2nd, & 3rd John, and the book of Revelation.
John originally ministered in Jerusalem. Early church tradition tells us that he left Jerusalem (probably well ahead of the destruction of the temple in A.D. 70) and went to the Roman province of Asia. There he ministered in and around Ephesus and probably with all of the seven churches of Asia described in Revelation 2 and 3.
The date of writing was most likely about A.D. 95. John, the aged father of the churches wrote to his beloved children.
The purpose of John's writings was to reassure these Christians, who were living in a difficult pagan environment, that they were indeed the children of God. It was further an encouragement for these believers to love one another in true Christian fellowship. There were also warnings about both internal and external threats of false teaching, insincere Christian living, and the difficulty of sin in the believer's life.