Ali ibn Abu'l-Hayja 'Abdallah ibn Hamdan ibn al-Harith al-Taghlibi (Arabic: سيف الدولة أبو الحسن ابن حمدان‎‎), more commonly known simply by his laqab (honorific epithet) of Sayf al-Dawla ("Sword of the Dynasty"), was the founder of the Emirate of Aleppo, encompassing most of northern Syria and parts of western Jazira, and the brother of al-Hasan ibn Abdallah ibn Hamdan (better known as Nasir al-Dawla).

The most prominent member of the Hamdanid dynasty, Sayf al-Dawla originally served under his elder brother in the latter's attempts to establish his control over the weak Abbasid government in Baghdad during the early 940s CE. After the failure of these endeavours, the ambitious Sayf al-Dawla turned towards Syria, where he confronted the ambitions of the Ikhshidids of Egypt to control the province. After two wars with them, his authority over northern Syria, centred at Aleppo, and the western Jazira, centred at Mayyafariqin, was recognized by the Ikhshidids and the Caliph. A series of tribal rebellions plagued his realm until 955, but he was successful in overcoming them and maintaining the allegiance of the most important Arab tribes. Sayf al-Dawla's court at Aleppo became the centre of a vibrant cultural life, and the literary cycle he gathered around him, including the great al-Mutanabbi, helped ensure his fame for posterity.

Sayf al-Dawla was widely celebrated for his role in the Arab–Byzantine Wars, facing a resurgent Byzantine Empire that in the early 10th century had begun to reconquer Muslim territories. In this struggle against a much superior enemy, he launched raids deep into Byzantine territory and managed to score a few successes, and generally held the upper hand until 955. After that, the new Byzantine commander, Nikephoros Phokas, and his lieutenants spearheaded an offensive that broke Hamdanid power. The Byzantines annexed Cilicia, and even occupied Aleppo itself briefly in 962. Sayf al-Dawla's final years were marked by military defeats, his own growing disability as a result of disease, and a decline in his authority that led to revolts by some of his closest lieutenants. He died in early 967, leaving a much weakened realm, which by 969 had lost Antioch and the Syrian littoral to the Byzantines and become a Byzantine tributary.

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