King David's trusted advisor who later betrayed him. He joined Absalom's plan to take over the kingdom. People thought Ahithophel's advice was very wise, almost like God's words (2 Samuel 16:23).
When David heard that Ahithophel betrayed him and joined Ahithophel, David prayed, "O LORD, please turn the counsel of Ahithophel into foolishness!" (2 Samuel 15:31). Ahithophel advised Absalom to take David's concubines (2 Samuel 16:20–22). Taking the king's concubines was a public act declaring that the former king was replaced.
Since David was still alive, this act aimed to create a final break between David and Absalom. It also fulfilled Nathan's prophecy to David that because David had taken another man's wife in secret, his own wives would be taken from him in public (2 Samuel 12:7–12).
Ahithophel's second plan was to attack David quickly with 12,000 skilled soldiers (2 Samuel 17:1–3). However, Absalom did not follow this advice. Instead, he listened to Hushai, who was secretly working for David. Hushai suggested a bigger attack plan (2 Samuel 17:4–14). His speech was meant to make Absalom feel important and give David more time to prepare. When Ahithophel saw that Absalom did not follow his advice, he went back to his hometown and killed himself (2 Samuel 17:23).