Albert Barnes Commentary 1 Kings 16:9

"And his servant Zimri, captain of half his chariots, conspired against him. Now he was in Tirzah, drinking himself drunk in the house of Arza, who was over the household in Tirzah:" — 1 Kings 16:9 (ASV)

The conspiracy of Zimri—Elah’s “servant” (that is, his “subject”)—was favored by his position, which probably gave him military authority in the city. It was also aided by the absence of a large portion of the people and their officers at Gibbethon, who might have stopped him (1 Kings 16:15), and by the despicable character of Elah. Instead of going to war, Elah continually reminded people of his low origin through conduct unworthy of a king.

Steward. The office was evidently one of considerable importance. In Solomon’s court, it conferred the rank of prince (שׂר śar). In Persia, the “steward of the household” sometimes acted as a type of regent during the king’s absence.