Abu Al-Hasan 'Ali ibn 'Othman (c. 1297 – 24 May 1351), (Arabic: أبو الحسن علي بن عثمان) was a sultan of the Marinid dynasty who reigned in Morocco between 1331 and 1348.

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.

The Castilians 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.

The food had run out and the townspeople and garrison had been reduced to eating their own shields, belts and shoes in an attempt to gain sustenance from the leather from which they were made.

[10] His brothers were captured and killed and the Sultanate of Tlemcen (covering roughly modern western half of Algeria) was annexed by the Marinids.

Abu al-Hasan received delegates from Egypt, Granada, Tunis and Mali congratulating him on his victory, by which he had gained complete control of the trans-Saharan trade.

[11] Flush from these victories, in 1339, Abu al-Hasan received an appeal from the Nasrid ruler Yusuf I of Granada to help drive back the Castilians.

The assembly of a large Marinid invasion force in Morocco prompted the Castilian king Alfonso XI to bring to an end his quarrel with Afonso IV of Portugal.

With the sea now clear for an invasion, Abu al-Hasan spent the rest of the summer calmly ferrying his troops and supplies across the straits to Algeciras.

In the meantime, Afonso IV of Portugal led an army overland to join Alfonso XI of Castile near Seville, and together they moved against the besiegers at Tarifa.

In a campaign in early 1347, Abu al-Hasan's Moroccan army swept through Ifriqiya and entered Tunis in September, 1347.

By uniting Morocco, Tlemcen and Ifriqiya, the Marinid ruler Abu al-Hasan effectively accomplished the conquest of dominions as great as the Almohad empire of the Maghreb, and the comparison was not lost on contemporaries.

[10] Abu al-Hasan's fleet was wrecked on its homeward journey by a tempest off Bougie, and the once mighty sultan was left stranded in the heart of enemy territory.

He managed to gather enough forces to attempt a march to recover Tlemcen, but was defeated by the resurgent Abdalwadid princes near the Chelif River.

As many of his former supporters defected, Abu al-Hasan was forced to proceed to Sijilmassa, in southern Morocco, which he hoped to use as a base to recover his sultanate.