Saint Deiniol (died c. 584) is a Christian saint from the country of Wales. Very little is known of the saint's life, but he is reported to be the first Bishop of Bangor, consecrated in 516 by Saint Dubricius , and he is the founder of the monastery of Bangor-on-Dee (Bangor Iscoed or Is-y-coed), Flintshire. The church of Hawarden in Flintshire is dedicated to him. William Gladstone dedicated Saint Deiniol's Library, a library for arts students, in 1896. Deiniol's feast day is September 11.