John the Apostle
John 21:7ESV·traditional attribution

That disciple whom Jesus loved therefore said to Peter, “It is the Lord!” When Simon Peter heard that it was the Lord, he put on his outer garment, for he was stripped for work, and threw himself into the sea.

John Calvin Reformed @genevareformer

7. Therefore the disciple whom Jesus loved saith to Peter. The Evangelist shows, by his example, that it is our duty to raise our hearts to God, whenever we succeed in any thing beyond our expectation; because we ought instantly to remember that this act of kindness has flowed from the favor of Him who is the Author of every blessing.

Matthew Henry Presbyterian @wholebiblehenry

We have here an account of Christ's appearance to his disciples at the sea of Tiberias. Now, 1. Let us compare this appearance with those that went before, In those Christ showed himself to his disciples when they were met in a solemn assembly (it should seem, for religious worship) upon a Lord's day, and when they were all together, perhaps expecting his appearing; but...

Commenting on John 21:1-14

John Gill Reformed Baptist @doctorgill

Therefore that disciple whom Jesus loved,.... Which was John the Evangelist and Apostle, the writer of this Gospel: saith unto Peter, it is the Lord; which two disciples were very intimate with each other, and communicated their thoughts freely to one another.