Here's the verse form 1 Peter 5:12 -- "Through Silvanus, our faithful brother (for so I regard him), I have written to you briefly, exhorting and testifying that this is the true grace of God. Stand firm in it."
So, he was very closely connected to both Peter and Paul. And if you're interested here's some more references to him:
2 Corinthians 1:19 -- he preached with Paul and Timothy
Acts 15:22 -- he was leading men in the church and was chosen to go with Paul to Antioch
1 Thessalonians and 2 Thessalonians 1:1 -- part of Paul's ministry.
He was a learned man. He was comfortable with Jews and Gentiles. According to a baby name website, Silvanus is a latin name and means Forest Dweller.
When you read about "Silas" that is the same guy. Silas is short for Silvanus.
He was the one in prison with Paul when they sang and praised God (Acts 16).