The book of 1 Corinthians was written by the apostle Paul. He authored this epistle near the end of his three-year stay in Ephesus, around A.D. 55-56, during his third missionary journey

. The letter also mentions a co-author, Sosthenes, who may have served as Paul's scribe or companion, but Paul is clearly the primary author of the content

. Paul wrote 1 Corinthians to address various issues in the Christian church in Corinth, such as divisions, immorality, misuse of spiritual gifts, and doctrinal misunderstandings. He had a personal relationship with the Corinthian believers, having founded the church there, and wrote this letter to restore them to faithfulness in Christ

. The authorship of Paul is supported by internal textual evidence, early manuscript traditions, and the consistent testimony of early church leaders. The letter begins with Paul's name and apostleship, and throughout the text, Paul refers to his personal connection and authority over the Corinthian church

. In summary, 1 Corinthians is widely accepted by scholars and Christian tradition as a letter composed by the apostle Paul, with Sosthenes mentioned as a co-sender or assistant