I Tertius, who wrote this epistle,.... This name is a Latin one, and perhaps the person might be a Roman, for the names Secundus, Tertius, Quartus, Quintus, &c. were common with the Romans; unless it may be thought, as it is by some, that this man was the same with Silas, who was a constant companion of the apostle; and the Hebrew word vlv is the same as Tertius; he also is numbered among the seventy disciples, and said to be bishop of Iconium; See Gill on "Lu 10:1".
Whosoever he was, it is certain he was an amanuensis of the apostle, who wrote this letter, either from the apostle's notes, or from his mouth.Salute you in the Lord.