Jehu is King,

2 Kings 9:1-13

    1 And Elisha the prophet called one of the sons of the prophets, and said to him, "Get yourself ready, take this flask of oil in your hand, and go to Ramoth Gilead. 2 Now when you arrive at that place, look there for Jehu the son of Jehoshaphat, the son of Nimshi, and go in and make him rise up from among his associates, and take him to an inner room. 3 Then take the flask of oil, and pour it on his head, and say, 'Thus says the LORD: "I have anointed you king over Israel."' Then open the door and flee, and do not delay."
    4 So the young man, the servant of the prophet, went to Ramoth Gilead. 5 And when he arrived, there were the captains of the army sitting; and he said, "I have a message for you, Commander."  Jehu said, "For which one of us?"  And he said, "For you, Commander." 6 Then he arose and went into the house. And he poured the oil on his head, and said to him, "Thus says the LORD God of Israel: 'I have anointed you king over the people of the LORD, over Israel. 7 You shall strike down the house of Ahab your master, that I may avenge the blood of My servants the prophets, and the blood of all the servants of the LORD, at the hand of Jezebel. 8 For the whole house of Ahab shall perish; and I will cut off from Ahab all the males in Israel, both bond and free. 9 So I will make the house of Ahab like the house of Jeroboam the son of Nebat, and like the house of Baasha the son of Ahijah. 10 The dogs shall eat Jezebel on the plot of ground at Jezreel, and there shall be none to bury her.'" And he opened the door and fled.
    11 Then Jehu came out to the servants of his master, and one said to him, "Is all well? Why did this madman come to you?"  And he said to them, "You know the man and his babble."  12 And they said, "A lie! Tell us now."  So he said, "Thus and thus he spoke to me, saying, 'Thus says the LORD: "I have anointed you king over Israel."'"  13 Then each man hastened to take his garment and put it under him on the top of the steps; and they blew trumpets, saying, "Jehu is king!"

Jehu (meaning "Jehovah is He") was chosen by God to be king in place of Joram who was busy defending Ramoth Gilead against Hazael the king of Syria.  Elisha sent a prophet to anoint with oil him as king in the name of the LORD, but did it in secret.  When Jehu’s servants asked what that was all about, they initially heard that it was babbling but knew that was not true; then he told them and they rejoiced and celebrated him as king.  Jehu was chosen to replace and defeat this remaining descendant of evil Ahab who had refused to destroy the enemies of the LORD (1 Kings 20:42) and had allied with Jezebel who was to be eaten by dogs for having a man killed for the land of his inheritance (1 Kings 21:15, 23, 25-26).  They together had caused Israel to sin in disobedience and abandonment of the LORD and His word, and now would all be stopped from continuing to do so.  The evil Ahab was no longer in charge; Jehu was king!  His name was a reminder that the LORD rules over all.