King Ahab is the king of Israel in the Book of Kings, which is part of the Hebrew and Christian Bible. He is considered to be one of the most evil kings in Israel. This is attributed to his alliance with his equally evil wife Jezebel.
Ahab succeeded the throne of Israel after King Omri, his father. Israel, at the time, was split from the rival southern kingdom of Judah. However, they were united by Yahwism, their national religion. Upon coronation, he married Jezebel, the daughter of King Ethbaal, a Phoenician king. The previous Israelite kings were consistently criticized for their corruption, especially in religious matters, as they promoted calf worship at Bethel and Dan, in the name of Yahweh. This was seen by Yahwist prophets as blasphemously corrupting "true Yawhism". As a result, Israel suffered from plagues of assassinations and chaos as divine punishment.
However, Ahab took a step further in religious corruption by actively promoting the worship of a completely foreign god named Baal. Although he was widely worshiped in Jezebel's homeland, Baal would retrospectively be scorned as a demon-like entity in the eyes of Jews and Christians. The Bible implies that Ahab did this simply for the sake of being evil/shock value. His evil was so widespread that one of his citizens, Hiel of Bethel, rebuilt the walls of a cursed city named Jericho, causing his sons to die.
Eventually, Elijah, a Yahwist prophet, confronted Ahab's sleazy behavior and declared a 3-year drought. Elijah eventually hid himself after this declaration. This was because Jezebel was actively killing most of Yahweh's prophets, which Ahab condoned. Ahab also ordered his servants to find Elijah and if they failed to find him, they were forced to swear, via an oath, that they told the truth. If found lying, they were executed. After the drought, Elijah challenged Ahab to a challenge, where Baalist prophets and himself would compete on which god would burn a bull sacrifice. Yahweh succeeded, which caused Ahab to humble himself.
Later on, Yahweh tried to get Ahab to recognize and worship Him only by granting him a military victory over Ben-Hadad (and his 32 king alliance), an Aramean king who wished to plunder his capital, wives and children. Ahab was understandably uncomfortable with what Ben-Hadad wanted and thus, warred against him, killing many of his soldiers. However, Ahab gave into Ben-Hadad's influence when the latter promised to give him back the cities his father conquered and establish bazaars in his hometown of Damascus. A prophet then confronted him about sparing Ben-Hadad, who was to be killed under divine commands. This also exposed Ahab's hypocrisy as he previously criticized the prophet for failing to fulfill his conditions to a man he guarded. However, this was a ruse to test Ahab's integrity as a ruler.
Ahab then grew sullen and presumably, his mental health also declined. This was seen in his overreaction and depressive episodes after one of his neighbours, Naboth, refused to sell his vineyard to him. He felt so pathetic and torn that he relied upon Jezebel to cheer him up, which she did by sadistically arranging Naboth's unjust execution. Elijah soon confronts him, and says that God would punish him and Jezebel. Ahab then finally comes to his senses and repents, which the Hebrew God takes notice of and relays it to Elijah. Ahab unfortunately lapses into his sinful ways as he gathers his false prophets, whom God allowed to be possessed by "lying spirits", to finally turn Ahab over to his transgressions. All of them responded, "Fight, and be successful" in battle of Ramoth-Gilead. The prophet Micaiah, whom Ahab recognizes is a true prophet but nonetheless despises, sarcastically repeats the other prophets' responses, but then gives his true message. He says that God was planning to have Ahab die in the battle. Ahab later disguises himself in the battle, but is shot by a stray arrow. It was later stated in the Hebrew Bible that dogs later licked up his blood.