Alexander O'Reilly, count, a Spanish soldier, born in Ireland about 1725, died in Spain in 1794. He entered the Spanish service at an early age, and was wounded in Italy during the war of the Austrian succession. He afterward served in the Austrian and French armies, reentered the Spanish service, and was made a brigadier. He introduced German tactics into the Spanish army, and was sent to Havana, where he restored the fortifications and was made inspector general. In 1765 he saved the life of the king during an outbreak at Madrid. On the expulsion of Ulua by the French colonists of Louisiana, O'Reilly was sent there with a fleet in 1708, and began by trying Lafreniere and other popular leaders by court martial and putting them to death for a crime against Spanish authority before Spain had formally taken possession. He then abolished the French laws and substituted those of Spain, with a new black code. A year after he returned to Spain, where all his acts were approved. He commanded an unsuccessful expedition against Algiers in 1775, and was next commandant general of Andalusia and governor of Cadiz, but was for a time in disgrace.

In 1794 he was called to command the army of the eastern Pyrenees, but died on the way.