Abu Al-Hasan 'Ali ibn 'Othman (c. 1297 – May 24, 1351) (Arabic: أبو الحسن علي بن عثمان‎‎) was a sultan of the Marinid dynasty who reigned in Morocco between 1331 and 1348. In 1333 he captured Gibraltar from the Castilians, although a later attempt to take Tarifa in 1339 ended in fiasco. In North Africa he extended his rule over Tlemcen and Ifriqiya, which together covered the north of what is now Algeria and Tunisia. Under him the Marinid realms in the Maghreb briefly covered an area that rivaled that of the preceding Almohad Caliphate. However, he was forced to retreat due to a revolt of the Arab tribes, was shipwrecked, and lost many of his supporters. His son Abu Inan Faris seized power in Fez. Abu Al-Hasan died in exile in the High Atlas mountains.

Abu al-Hassan was the son of Marinid ruler Abu Sa'id Uthman II and an Abyssinian mother. He had a dark complexion, and was known as the 'Black Sultan' of Morocco. He succeeded his father Abu Sa'id Uthman II in 1331. Abu al-Hassan married Fatima, daughter of the Hafsid ruler Abu Bakr of Ifriqiya, sealing an alliance between the Marinids and Hafsids against the Zayyanid dynasty of Tlemcen.

In 1309, Castillian troops under Ferdinand IV captured Gibraltar, then known as the Medinat al-Fath (City of Victory), from the Muslim-ruled Emirate of Granada. In 1333, responding to the appeal of Nasrid ruler Muhammad IV of Granada, Abu al-Hassan sent a Moroccan army to Algeciras under the command of his son Abd al-Malik Abd al-Wahid. A force of 7,000 men was transported across the Strait of Gibraltar to rendezvous with the forces of Muhammad IV of Granada at Algeciras in February 1333. The Castillians were distracted by the coronation of King Alfonso XI and were slow to respond to the invasion force, which was able to lay siege to Gibraltar before much of a response could be organised.

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