Epistles - as from St. Paul, St. Peter. St. John, St. James and St. Jude.
They are called epistles
http://www.interfaith.org/christianity/apocrypha/
Three names for early church leaders in history are Peter, Paul, and James. Peter was one of the twelve apostles and a prominent leader in the early Christian church. Paul was a missionary who wrote many of the letters in the New Testament and played a key role in spreading Christianity. James, the brother of Jesus, was a leader in the church in Jerusalem and played a significant role in the early Christian community.
The Apostle Paul wrote most of the New Testament as letters to different churches. For instance: Galatians was written to a church in Galatia; Phillippians to a church in Phillippi; Corinthians to a church in Corinth, etc.
The earliest letter in the bible is the Letter by Paul to the church in Corinth.
The early leaders of the church decided the canon of the New Testament. These early leaders were Bishops in a number of cities in the Middle East.
An epistle.
Jesus was the leader through his chosen vicar - St. Peter. The other apostles also helped in the leadership of the early Church.
The early chuch leaders had at times more influence than the king. Through ignorance of the general public, the church was able to manipulate the common man into believing that the church had power over their souls. This being the case if the church said "Jump" the people did so for fear of disobedience to church leaders, and their being assigned to hell for their disobedience. Respectfully
The Acts of the Apostles which details the history of the early church is between the Gospel accounts and the epistles.
John Taylor was the third president of the Church of Jesus Christ of Latter-day Saints (the "Mormon" church), but his middle name was not Joseph. He converted to Mormonism six years after it began, so he wasn't one of the original leaders, but he was an early leader. I couldn't find any record of a John Joseph Taylor being an early leader in the Mormon Church.
St. Paul, St. Peter, St. John, St. Jude all wrote epistles. St. James also wrote an epistle but it is uncertain if he was James the greater, James the lesser or another James.