Imad ad-Din Zengi (also Zangi or Zengui) (1087-1146) was the son of Aq Sunqur al-Hajib, governor of Aleppo under Malik Shah I. He became atabeg of Mosul in 1127, and of Aleppo in 1128, uniting the two cities under his personal rule, and was the founder of the Zengid dynasty.
During his reign he was in conflict with the Burids, from whom he captured Emesa in 1138. Later that year, Byzantine EmperorJohn II Comnenus besieged Aleppo, after he had brought the Crusader Principality of Antioch under Byzantine control. This siege was unsuccessful, and Zengi turned his attention to Damascus in 1139. Damascus allied with the Crusader Kingdom of Jerusalem against him, and he was unable to take the city.
In 1144 Zengi besieged the Crusader County of Edessa. Edessa was the weakest and least Latinized Crusader state, and Zengi captured it on December 24, 1144. This event led to the Second Crusade, and later Muslim chroniclers noted it as the start of the jihad against the Crusader states.
Though he continued his attempted to take Damascus, Zengi was assassinated by a slave in 1146. In Mosul he was succeeded by his eldest son Saif ad-Din Ghazi I and in Aleppo he was succeeded by his second son Nur ad-Din.
According to Crusader legend, Zengi's mother was Ida of Austria (mother of Leopold III of Austria), who had supposedly been captured during the Crusade of 1101 and placed in a harem.
In 1031 Edessa was given up to the Byzantines by its Arab governor.
It was retaken by the Arabs, and then successivelly held by the Greeks, the Seljuk Turks (1087), the Crusaders (1099), who established there the County of Edessa and kept the city until 1144, when it was again captured by the Turk Zengui, and most of its inhabitants were slaughtered together with the Latin archbishop.
These events are known to us chiefly through the Armenian historian Matthew, who had been born at Edessa.