In Greek, both men and gods can be called episkopoi, when referring to an “overseer”.
Biblically however, the term is most often translated “Bishop” and is applied pre-eminently to Christ as “Shepherd and Bishop of our souls” (1Peter 2:25).
It is also applied  to the Apostles, speaking of Judas, “and his bishopric (episkope) let another take” (Acts 1: 20), and to designated leaders of a congregation when identifying bishops (episkopos) and deacons in the church (Philippians 1:1). 

The term ‘Bishop’ therefore applies to an overseer of high office. Whilst the Apostle’s office was initially referred to as   episkope, it appears they were not called bishops. Scripture tells us that they were recognized as Apostles who “gave themselves continually to prayer and to the ministry of the word” (Acts 6:4).  

In the first period of the early Church, Christians primarily looked for evidence of God’s works in a believer (as Christ worked), not necessarily in an administrative office. Unlike the authoritive style of Rome, the apostles treated their fellow Christians as brethren, (rather than as mere subjects), administering their authority according to Peter's instruction to the elders wherein he stated "not as being lords over God's heritage, but by being examples to the flock" (1 Pet 5:3).  

Originally, it was from the synagogue that the name presbyter (presbyteros - presbuvtero") was borrowed. Its literal meaning in Greek is “elder”.
The Church, which was originally in Jerusalem (and of synagogue administration by nature), simply transferred the title. The Episcopal title of episkopos  (ejpivskopo"), on the other hand was of gentile origin (having been used previously among the Greek pagan overseers). When persecution dispersed the Church in the first and second century into the gentile world, episkopos became the title of choice. Therefore, originally, both bishop and presbyter related to the same office.  

This is qualified by the New Testament not appearing to recognize any clear distinction between them. The words ‘Presbyter’ and ‘Bishop’ are used interchangeably. For example, in Acts Paul calls the same body in one instance presbyters (20:17), and in another, bishops (20:28). Paul also directs Titus to ordain presbyters (presbuvtero"); but when he charges them to feed the Church of God and warns them of pending false brethren, he addresses them using the Greek word episkopos (bishop). Peter also uses both terms in a way that implies they were the highest authority in the local church, without identifying any office between them and the apostle/prophet (1Pet 5:1-2). 

Some believe the presbyter/bishop initially occupied the position of administration, rather than that of teaching; however teaching was always a biblical attribute of the calling. In fact bishops were instructed to teach sound doctrine to combat both heretics and those who opposed the gospel (Titus 1:9). This is also supported by the “apt to teach” bishopric qualification which Paul outlined in his letter to Timothy (1Tim 3:2). It seems, according to early writers, that initially no single person delegated these positions. Clement of Rome testified that "the ministry office of the bishop was appointed with the consent of the whole church". 

It wasn’t until late in the first century that the letters of Ignatius (picture), Bishop of Antioch, gave reference of a “single ruling bishop” in each city, and indicated that the role of the bishops, as delegates, was primarily to express concerns between the churches.
Individual ruling bishops in the Church, about this time, became a locally recognized authority. While Ignatius’s writings didn’t claim the office as a divine ordinance, he nevertheless insisted on it in his region to help prevent schism in the Church. He was also the first writer to use the word ‘Catholic’ (meaning- universal) in describing the Church, perhaps as a result of the bishopric network. At the time, ‘Catholic’ had quite a different meaning to what developed later as “Roman Catholic”. 

The elevation of the Bishop title above that of the term Presbyter slowly developed between 70 – 120AD. We know the office and its authority was strengthened by its regular doctrinal conflicts with the Gnostics and other heretics of the time.
Another factor in the authoritive recognition of the local church Bishop was with the eventual dividing up of his tasks, perhaps as a result of growing congregations. Historical records indicate that initially Presbyters/Bishops oversaw the sacraments and worship, while the deacons supported them in those duties. 

By the late second century the unchallenged overseer of the local church was the Bishop, and the size of the bishop’s office began to denote his power and authority. This changed the perception of the office even amongst bishops themselves, as the founding principles slowly departed from the original biblical purpose of its calling.
As a result, three differing views of the office arose. 

1.   The office, on principle, was a serious departure from scripture, and should be realigned.

2.   The Church government was merely exercising the liberty they had to combat heresy and adjust to modern times.

3.   The evolved perception that God so in-dwelt the Church, that any change was the work of God and therefore must be submitted to.

During the persecutions of the second and third centuries, the question of re-admittance to the Church for those who had committed apostasy was fiercely debated. With this, and the advance of various Christian heretics, the bishop was looked upon more and more to issue edicts of doctrine and policy.
For example, the first record of penitent adulterers being received back as a matter of Church policy came in the third century from the Bishop of Rome, Callistus (217-222). Despite conceiving the doctrine from an interpretation of a single text, he nevertheless insisted “the Church of Rome was the heir of Peter, to whom the Lord had given the keys to bind and loose the sins of men”.
This marked the first record of the Church claiming an authority to bind or loose the sins of men with regard to availing or withholding Church body membership and salvation.
Having received such a powerful autocratic status, the local Bishop’s role quickly changed. This new biblically discordant status would dominate the entire Western European society for the next 1500 years.

After the Constantinian Revolution in the fourth century bishops began to be recognised and treated like kings. The role and status of the bishop was elevated as politics entered the once persecuted Church. The politically ambitious, believers still half rooted in Greek pagan practice, and those spiritually apathetic massed to the official religion seeking prominence and favor from an emperor who preferred the peaceful ethic of Christianity. 

In time the senior bishop overseeing major empire cities became known as a ‘Patriarch’ and held much respect and authority.
In all there were four Patriarchs: Rome, Constantinople, Antioch and Alexandria. A fifth, in Jerusalem, was recognised as an honorary Patriarch.
Today, Nazareth born and of Arab ethnicity, Latin Patriarch Michel Sabbah, as Archbishop of Jerusalem and head of the local Roman Catholic Parish, holds this office. However his support of the 2000 Al Aqsa Intifada and refusing to acknowledge Israel as a Jewish State has drawn criticism among many Christian groups. King Carlos of Spain currently holds the title “King of Jerusalem”.

The authority of the episkopoi (bishop) after the Constantine Revolution became the issue of significant conflict. In fact, in time a power-play between the Bishop of Rome and the church of the East was to play a key part in their schism and eventual split in 1054.  

In 382AD, during a Roman synod, Bishop Damasus (picture) declared, for the first time, “preeminence and primacy of the Roman Church above other sees”. This was not based upon any patriarchal synod or council, but again by Rome’s interpretation of Math 16, enforcing its “Primacy of Peter” dogma.
This declaration of preeminence was quietly assumed until 440AD when the Bishop of Rome, Leo I (the Great), was announced “Pope” (Pontus Maximus) whereupon it was cemented as constitutional Roman Catholic doctrine. 

Pope Leo, (picture) after securing the safety of the people and buildings during the sacking of Rome in 410AD, and the fall of Rome in 452AD, took the Bishopric of Rome to a new level when he demanded allegiance from all the other Bishops and Patriarchs (as have all his successors thereafter).
Such was the Roman bishop’s influence upon Europe that from this time the the Church, from this time, was re-named the “Roman Catholic Church”. It began to formulate its doctrines and rulership more aggressively and authoritatively. The dogma asserting the bishop of Rome’s authority over all other bishops remains today, and is called “The Petrine Supremacy”. 

For the next 1000yrs the Papal Bishop’s office saw extremes of absolute and unchallenged power, cruelty, and corruption (including the murder of more Christians and Jews than any other regime, including Islam). Ironically, it was also instrumental in preserving Christianity by protecting it from the many heresies that opposed it.

It wasn’t until after the scourge of the Black Plague had taken fifteen million souls during the 14^th C, and the influence of the Renaissance, that many of Europe’s populace gained the courage to challenged the Roman bishop’s office which allowed opportunity for reform.
The rise of the Protestant Churches as a result of the Reformation saw Church offices slowly return to the five fold ministry names like Pastor etc outlined in Ephesians 4:11. John Calvin, Huldrych Zwingli, and other Reformers revived the Pastoral term with their followers mainly to avoid association with corrupt Catholic priests.
This change was embraced further in England when Oliver Cromwell, in the 17^th century, supported the idea of a national Church including Scotland and Ireland, and void existing papal bishopric hierarchy entirely.  

Today, the title and office of pastor and teacher in Protestant churches bear a close relation to the first century ordination of Bishop.
The use of the term Pastor originally stemmed from the OT Hebrew word רעה (ra-ah). This word is used 173 times, sited as early as Genesis (29:7), and is used to describe the care of a shepherd “feeding” sheep. The most commonly referenced passage is that of Jeremiah 3:15, "And I will give you Pastors according to mine heart, which shall feed you with knowledge and understanding".
In the NT, the Greek equivalent to [ra-ah] is ποιμήν (poimēn) and is used 18 times and also translated Pastor or Shepherd.
It was from the word presbyter the term ‘Priest’ was derived, and has since been a popular term among many and varied religious societies outside the Church throughout history Catholic and Eastern Orthodox churches still generally refer to their leaders as priests (although the term pastor may also be used, particularly in North America). Anglican churches still rarely use the term "pastor", preferring the words rector and vicar.
Whilst priest is not a common term within the Protestant lineage, the believers “priesthood” is affirmed as a scriptural identity for all true servants of Jesus Christ (1Pt 2:9).