The "beloved disciple" was the moniker given to St. John, the Apostle and Evangelist. With his brother, James, they were the sons of Zebedee, and together, they were called "Boanerges" or "Sons of Thunder" by the Lord Jesus Himself. With these names as ascribed, what can we make of St. John?
Clearly, he was one of the twelve disciples classically called by the Lord - right amid his work and career, causing him to leave everything (and, in this case, his father Zebedee) behind to follow the Master. That Jesus called them "Sons of Thunder" indicates that James and John were a force to be reckoned with and perhaps a little ambitious, too, as evidenced by the infamous request made through their mother to give seats on the left and right side of the Lord when He comes into his Kingdom.
The "beloved disciple" title should not imply any favouritism on the part of the Lord but a reminder that, as this was how God the Father addressed Jesus at His baptism, anyone who leaves everything to follow Christ is similarly baptised as the beloved of God. God willed that John was the first among the disciples to understand the meaning of Jesus' resurrection. Seeing the empty tomb and the left-behind death shrouds, all the things that Jesus said about His death and rising to new life fell into place, eliciting an insight that caused John to believe in a way that was humanly impossible otherwise.
In his later years, John was moved to write his memories of the Lord as the Gospel of Jesus Christ.
St. John, the Evangelist, pray for us!