Alexander Riley (1778 – 17 November 1833) was a merchant and one of the most important early pastoralists in Sydney and in New South Wales. Born in London to , a well-educated bookseller, and Margaret Raby, he was the older brother of Edward Riley, also a merchant and pastoralist in Sydney. In 1804 Riley followed two of his sisters, who had married captains in the New South Wales Corps, and Anthony Fenn Kemp, to Australia where, with his brother Edward who later followed, they went on to become two of Australia's richest men.