Luke
Acts 9:1ESV·traditional attribution

But Saul, still breathing threats and murder against the disciples of the Lord, went to the high priest

John Calvin Reformed @genevareformer

1. And Saul. Luke setteth down in this place a noble history, and a history full well worthy to be remembered, concerning the conversion of Paul; after what sort the Lord did not only bring him under, and make him subject to his commandment, when he raged like an untamed beast but also how he made him another and a new man.

Matthew Henry Presbyterian @wholebiblehenry

We found mention made of Saul twice or thrice in the story of Stephen, for the sacred penman longed to come to his story; and now we are come to it, not quite taking leave of Peter but from henceforward being mostly taken up with Paul the apostle of the Gentiles, as Peter was of the circumcision.

Commenting on Acts 9:1-9

Albert Barnes Presbyterian @notesbybarnes

Chapter 9 Introduction: This chapter commences a very important part of the Acts of the Apostles--the conversion and labours of Saul of Tarsus. The remainder of the book is chiefly occupied with an account of his labours and trials in the establishment of churches, and in spreading the gospel through the Gentile world.