John the Apostle
2 John 1:1ESV·traditional attribution

The elder to the elect lady and her children, whom I love in truth, and not only I, but also all who know the truth,

Matthew Henry Presbyterian @wholebiblehenry

Ancient epistles began, as here, with salutation and good wishes: religion consecrates, as far as may be, old forms, and turns compliments into real expressions of life and love. Here we have, as usually, I. The saluter, not expressed by name, but by a chosen character: The elder.

Commenting on 2 John 1:1-4

John Gill Reformed Baptist @doctorgill

The elder unto the elect lady and her children,.... By the "elder" is meant the writer of this epistle, the Apostle John, who so calls himself either on account of his age, he being now near an hundred years of age, having outlived all the apostles: or on account of his office, being a bishop or overseer, not only of the church at Ephesus, but...

Albert Barnes Presbyterian @notesbybarnes

INTRODUCTION TO THE SECOND AND THIRD EPISTLES OF JOHN, I.---THE AUTHENTICITY OF THE SECOND AND THIRD EPISTLES OF JOHN. THE authenticity of these two epistles was doubted by many in the early Christian church, and it was not before a considerable time had elapsed that their canonical authority was fully admitted.