Zimri was the chariot commander of Baasha's army who killed Elah when he was getting drunk, took over the throne and then proceeded to slaughter Baasha's entire family.
Zimri, one of his officials, who had command of half his chariots, plotted against him. Elah was in Tirzah at the time, getting drunk in the home of Arza, the man in charge of the palace at Tirzah. Zimri came in, struck him down and killed him in the twenty-seventh year of Asa king of Judah. Then he succeeded him as king.
(1 Kings 16:8-10)
It seemed like Zimri acted without his army's support because his reign ended barely seven days after it began. Omri, whom the army elected as king, laid siege to Tirzah, whereupon Zimri set fire to the palace and perished amid its ruins. Omri succeeded to the throne only after four years of fierce war with Tibni, another claimant to the throne.