Raynald of Châtillon (also Reynald or Reginald of Chastillon) (died July 4 118) was a knight who served in the Second Crusade and remained in the Holy Land after its defeat. There he ruled as Prince of Antioch from 1153 to 1160.

He was a younger son of Henry, lord of Châtillon, from the middle-ranking noble family of Champagne that had produced Eudes of Châtillon, Pope Urban II. Raynald had joined the Second Crusade in 1147 to seek his fortune. He entered the service of Constance of Antioch, whose first husband had died in 1149. She married Raynald in secret in 1153, without consulting her liege lord, Baldwin III of Jerusalem. Neither King Baldwin nor Aimery of Limoges, the Latin Patriarch of Antioch, approved of Constance's choice of a husband of such lower birth.

One of Raynald's first acts in Antioch was an assault on the Latin Patriarch; he had the Patriach seized, stripped naked, covered in honey, and left to suffer in the burning sun. When the Patriach was released, he collapsed in exhaustion and agreed to finance Raynald's expedition against Cyprus. Raynald's forces attacked Cyprus, ravaging the island, and raping and pillaging the inhabitants. Cyprus was a possession of the Byzantine Empire, and in 1159 Raynald was forced to pay homage to Byzantine emperor Manuel I Comnenus as punishment for his attack, promising to accept a Greek Patriarch in Antioch. When Manuel came to Antioch later that year to meet with Baldwin III, King of Jerusalem, Raynald was forced to lead Manuel's horse into the city.

Soon after this, in 1160, Raynald was captured by the Muslims during a plundering raid against the Syrian and Armenian peasants of the neighbourhood of Marash. He was confined at Aleppo for the next seventeen years. He was ransomed for the extraordinary sum of 120,000 gold dinars in 1176, emerging from his long captivity more bloodthirsty and ambitious than ever. Because his wife Constance had died in 1163, Raynald married another wealthy widow, Stephanie, the widow of both Humphrey III of Toron and Miles of Plancy, and the heiress of the lordship of Oultrejordain, including the castles Kerak and Montreal to the southeast of the Dead Sea. These fortresses controlled the trade routes between Egypt and Damascus and gave Raynald access to the Red Sea. He became notorious for his wantom cruelty at Kerak, often having his enemies and hostages flung from the walls of castle to be dashed to pieces on the rocks below.

In November 1177, at the head of the army of the kingdom, he defeated Saladin at the Battle of Montgisard; Saladin narrowly escaped. In 1181 the temptation of the caravans which passed by Kerak proved too strong, and, in spite of a truce between Saladin and Baldwin IV, Raynald began to plunder. Saladin demanded reparations from Baldwin IV, but Baldwin could only reply that he was unable to coerce his unruly vassal. The result was a new outbreak of war between Saladin and the Latin kingdom in 1182. In the course of the hostilities Raynald launched ships on the Red Sea, partly for piracy, but partly as a threat against Mecca and Medina, challenging Islam in its own holy places. He swore to defile the sacred cities, to drag the body of the Prophet Muhammad from his tomb, and to destroy the Kaaba. His pirates ravaged villages up and down the Red Sea, before being captured by the army of Al-Adil I only a few miles from Medina. Although Raynald's pirates were taken to Cairo and beheaded, Raynald himself escaped to the Moab. Saladin vowed to behead Raynald himself, and at the end of the year Saladin attacked Kerak, during the marriage of Raynald's stepson Humphrey IV of Toron to Isabella of Jerusalem. The siege was raised by Count Raymond III of Tripoli, and Reynald was quiet until 1186.

That year he allied with Sibylla and Guy of Lusignan against Count Raymond, and his influence contributed to the recognition of Guy as king of Jerusalem, although Raymond was the better candidate. Later in 1186 Raynald attacked a caravan in which Saladin's sister was travelling, breaking the truce between Saladin and the Crusaders. King Guy chastised Raynald in an attempt to appease Saladin, but Raynald replied that he was lord of his own lands and that he had made no peace with Saladin. Saladin swore that Raynald would be executed if he was ever taken prisoner.

In 1187 Saladin invaded the kingdom, defeating the Crusaders at the Battle of Hattin. The battle left Saladin with many prisoners. Most prominent among these prisoners were Reynald and King Guy, both of whom Saladin ordered brought to his tent. According to al-Safadi in al-Wafi bi'l-wafayat, Saladin offered water to Guy, who then gave the glass to Raynald. Saladin knocked the water away, saying that he had not offered water to Raynald and thus was not bound by the Muslim rules of hospitality. After being rebuked by Saladin for his treachery, Raynald was executed, either beheaded by Saladin himself or killed by one of Saladin's men in the presence of his companions. King Guy, however, was spared. Saladin explained that one king did not kill another and that Raynald had only been executed because of his great crimes. Guy was taken to Damascus for a time, then allowed to go free.

Many of the Crusaders considered Raynald a martyr, although all evidence shows him to have been a plunderer and a pirate who had little concern for the welfare of the Kingdom. The successes of the Kingdom were almost singlehandedly undone by Raynald's recklessness and selfishness.

Raynald and Constance had two daughters: Agnes, who married king Bela III of Hungary; and Alix, who married Azzo V d'Este.

A largely fictionalized version of Raynald is played by Brendan Gleeson in the 2005 movie Kingdom of Heaven