Adam Clarke on 1 Kings 13:1

There came a man of God - Who this was we know not. The Chaldee, Syriac, and Arabic call him a prophet. The Vulgate and Septuagint follow the Hebrew, איש אלהים ish elohim means a Divine person, one wholly devoted to God's service. Some have thought it was Shemaiah, others Joel, and others Iddo. It could not have been the latter, for he wrote the acts of Jeroboam, 2Chr 9:29, and the prophet was killed before he returned home; but conjecture is idle on such a subject.

Jeroboam stood by the altar - Like gods, like priest; he made himself high priest, and he took of the lowest of the people, and made them priests of the high places; they proved themselves to be fools by worshipping calves.