Church Fathers, the Early Christians (Irenaeus)

St. Irenaeus was probably born around 125 A.D. He was a disciple of Polycarp who was a disciple of John who was an apostle of Christ. He wrote the “Refutation of Heresies” against Gnostism and “Proof of the Apostolic Preaching.” 
Irenaeus wrote: 

"Where, then, do we look for Christ's authentic teaching? In the congregations that were founded by the apostles, who set trustworthy men in charge of them, and charged them to pass on the teaching unchanged to future generations through carefully chosen successors." 

He was probably the first to speak of the church as “Catholic.”

He wrote about Linus (the Pope who succeeded Peter and reigned from about 64 A.D. – 79 A.D.) around 180 A.D. saying: 

“The blessed apostles, then, having founded and built of the Church, committed into the hands of Linus the office of the episcopate.” (Against Heresies) 

This is the same Linus mentioned in Paul’s Second Letter to Timothy Chapter 4 versus 20-22. 

Here is the quote from 2nd Timothy chapter 4 from verse 18 -- it is the end of the letter. I have included the footnotes from the NAB. 

18

The Lord will rescue me from every evil threat and will bring me safe to his heavenly kingdom. To him be glory forever and ever. Amen.

19

Greet Prisca and Aquila ⁹ and the family of Onesiphorus.

20

Erastus ¹⁰ remained in Corinth, while I left Trophimus sick at Miletus.

21

Try to get here before winter. Eubulus, Pudens, Linus, ¹¹ Claudia, and all the brothers send greetings.

22

The Lord be with your spirit. Grace be with all of you.

Studying the earliest Christians is also helpful because you can see, from the very earliest years of the church, an apostolic lineage. From Peter to Linus to Cletus to St. Clement and so on . . . . until today with Benedict.

H/T - Angela, my dear friend and my Godchild's Mom 

For further resources:

St. Irenaeus: http://www.newadvent.org/cathen/08130b.htm

NAB  - New American Bible Online