Adam Clarke on Colossians 4:14

Luke, the beloved physician - This is generally supposed to be the same with Luke the evangelist. See the preface to the notes on this gospel. Some, however, suppose them to be different persons; because, where it is evident that Luke the evangelist is meant, he never has more than his simple name Luke; and because the apostle is supposed to intend a different person here, he adds, ὁ ιατρος ὁ αγαπητος, the beloved physician. The word ιατρος signifies a healer, and must not be restricted to physician, in the sense in which we use that word; he was surgeon, physician, and dispenser of medicines, etc., for all these were frequently combined in the same person.