Which false god did Ahab and Jezebel worship?

Answer: Baal

Ahab began to serve Baal and worship him.

“And as if it were not enough for him to walk in the sins of Jeroboam son of Nebat, he even married Jezebel the daughter of Ethbaal king of the Sidonians, and he then proceeded to serve and worship Baal.”— 1 Kings 16:31 (BSB)