1 Paul, Silvanus, and Timothy, to the assembly of the Thessalonians in God our Father, and the Lord Jesus Christ (WEB)
Paul is also known as Saul who persecuted the church before his transformation [Acts 8:1-3] and was used greatly by the Lord Jesus Christ after his conversion [Acts 9:1-18] to spread the Gospel, debate Judaizers who wanted the believers to go back to the law, and to plant churches.
Silvanus or Silas was a companion of Paul during his mission trips to Asia Minor [mordern day Turkey] and the establishment of the 7 churches spoken about in the Book of Revelation and through Greece [1 Corinthians 1:19].
Timothy was also a companion of Paul and would be dispatch by Paul to the churches like the one in Thessalonica to encourage them to continue in the faith and mission they have received from the Lord. In 1 Timothy 1:3, Paul sent Timothy to Ephesus to help stop some brethren from preaching and teaching false doctrine. Timothy was instrumental to Paul and the churches, helping the believers from drifting away from the truth.