Nur al-Din, also known as Nur ad-Din, was an influential and famous Muslim, whose life took place from 1118 to 1174. During his lifetime, the renowned Crusades were taking place, specifically the Second Crusade. Although Nur al-Din's significance in the Second Crusade was not little, he took an even more important role in the overall fight against the Christian forces. Nur al-Din's example as a man of justice, wisdom, and respect, was not exclusively for Muslims, but also for his enemies.
After the murder of Nur al-Din's father, Imad ad-Din Zengi (a fervent opponent of the crusaders), Nur al-Din assumed his rule over Aleppo, while his brother, Saif ad-Din Ghazi I, took kingship of Mosul. Nur al-Din did not waste time during his reign; he launched an attack on the Principality of Antioch, a crusader state. Additionally, Nur al-Din held his own when an effort to recover the once-crusader state County of Edessa was ensued by Joscelin II.
From early in his reign, it had been a goal of Nur al-Din to ally Muslim forces in order to focus on the challenge of the crusaders as opposed to each other. Fulfilling his hope to some extent, Nur al-Din established a treaty with the governer of Damascus, Mu'in ad-Din Unur. When the Christian forces came upon Damascus in 1148, resulting in the aid of Nur al-Din and his forces. Nur al-Din led attacks against the crusaders and crusader territories, which landed him a certain amount of importance and respect.
Nur al-Din took control of Mosul and Aleppo in 1149 upon the death of his brother, despite an heir to rulership. Nur al-Din is perhaps most famous for uniting the Muslims of Syria and Egypt, which aided the Muslim forces tremendously.
Phillips, Jonathan. The Second Crusade: Extending the Frontiers of Christendom. Yale University Press, 2007.
Riley-Smith, Jonathan. The Crusades: A History. Continuum International Publishing Group, 2005.