Origen

Origen (c 185 - c 254 AD) was born in Alexandria to Christian parents, who named him Origenes Adamantius.  His father Leonides was martyred in 202 AD, and Eusebius relates a story that young Origen wanted to be martyred with his father but was thwarted by his mother who hid his clothes.

Origen was a gifted teacher of the Scriptures and discovered this gift and passion at a young age.  At age 18 (203 AD), the bishop of Alexandria, Demetrius, appointed him to succeed Clement as the leader of the theological school there.  He performed this role for a dozen years until persecution in 215 AD forced him to flee.
Origen traveled through a number of places in his lifetime, including Rome, but he stayed the longest at Caesarea in Palestine.  There he was invited by the bishops to preach in their churches.
Despite his teaching experience and ability, Origen was still a layman and Demetrius was not happy that a layman from his city was preaching in churches in other cities, despite the approval of the local bishops.  He ordered him back to Alexandria, so Origen obeyed and he took up his position at the school.  However, in 230 AD Origen was on his way to Greece when he visited Caesarea again.  The bishops there ordained him, and this really got Demetrius upset.  When Origen returned, he was removed from his teaching position in the school and excommunicated from the church.
Origen returned to Caesarea and opened a new theological school, continued his writings and teaching, and spent the remainder of his life in Palestine.  During another persecution in 250 AD, he was arrested and tortured and died a few years later as a result.

From Origen's teachings and life events, we see the early church changing in the following ways.

1. Infant baptism is now commonly practiced.  Origen states in his commentary on Romans that infants were baptized in keeping with apostolic tradition, and his writings do not appear to show he disagreed with that tradition.
2. Church leadership was becoming formalized and separated from the rest of the people in the church.  The idea of clergy and laity had already become entrenched.  The fact that Origen was a more gifted teacher than many bishops did not matter to Demetrius, who excommunicated him for preaching in other churches and being ordained without his approval.  Laymen could teach in a school of theology, but not in a church!
3. Bishops had absolute authority over church affairs in their own city.  Demetrius excommunicated Origen not because the Christians in Alexandria found him behaving sinfully or because his theology was heretical, but simply because Demetrius was jealous of his abilities and his influence with other bishops.  
4. Bishops could determine arbitrarily who was part of Christ's church and who was not.  Again, Origen was not excommunicated for immorality but for simply breaking the rules of church procedure.  This is a novel development, for following church rules was never a requirement for being a Christian in the New Testament.
5. Despite Demetrius' absolute authority in the church in Alexandria, he appears to have had no authority in Palestine, where those bishops openly ignored his decisions and allowed Origen to open a new school and teach in their churches for the final 20 years of his life.  Therefore, churches in each city still operated somewhat independently, each under their own bishop.