Silvanus of the Seventy
Silvanus is mentioned in the New Testament (Acts, various letters of Paul, and 1 Peter) as a co-writer or transcriber of some of these works. He later became Bishop of Thessalonika and died a martyr.
In Eastern Orthodox tradition he is assumed to be one of the Seventy Apostles, those followers of Jesus sent out by him in Luke 10.
Silvanus is probably the same person as Silas, also mentioned in various places in the New Testament.