St. Polycarp served as the bishop of the church in Smyrna, one of the churches mentioned in The Apocalypse (Book of Revelation). He lived and served the Church during the time of the Apostles. St. Irenaeus of Lyon, who lived near the time of the Apostles, wrote this about St. Polycarp:
"Polycarp also was not only instructed by apostles, and conversed with many who had seen Christ, but was also, by apostles in Asia, appointed bishop of the Church in Smyrna, whom I also saw in myearly youth, for he tarried [on earth] a very long time, and, when a very old man, gloriously and most nobly suffering martyrdom, departed this life, having always taught the things which he had learned from the apostles, and which the Church has handed down, and which alone are true. To these things all the [churches in Asia] testify, as do also those men who have succeeded Polycarp down to the present time...." (Against the Heretics, Bk. III)
You may read The Martyrdom of Polycarp on the website of the Orthodox Metropolitanate of Hong Kong and Southeast Asia (Ecumenical Patriarchate). St. Ignatius, the second bishop of Antioch, wrote a letter to St. Polycarp, which can be read on the Early Christian Writings website. (On this site, a shorter version and a longer version are included, so you may want to skip the repeating paragraphs).