Jamieson, Fausset and Brown on 1 Kings 1:8

8. But Zadok the priest--He had been high priest in the tabernacle at Gibeon under Saul (1Ch 16:39). David, on his accession, had conjoined him and Abiathar equal in the exercise of their high functions (2Sa 8:17; 15:24, 29, 35). But it is extremely probable that some cause of jealousy or discord between them had arisen, and hence each lent his countenance and support to opposite parties.

Benaiah--Distinguished for his bravery (1Sa 23:20), he had been appointed captain of the king's bodyguard (2Sa 8:18; 20:23; 1Ch 18:17), and was regarded by Joab as a rival.

Nathan the prophet--He was held in high estimation by David, and stood on the most intimate relations with the royal family (2Sa 12:25).

Shimei--probably the person of this name who was afterwards enrolled among Solomon's great officers (1Ki 4:18).

Rei--supposed to be the same as Ira (2Sa 20:26).

and the mighty men--the select band of worthies.