Complex sentence: Robert Hunter (fl.1748--1780) was a portrait-painter, a native of Ulster, studied under the elder Pope, and had a considerable practice in Dublin in the middle of the eighteenth century.
Split into simpler sentences: Robert Hunter (fl.1748--1780) was a portrait-painter and a native of Ulster. He studied under the elder Pope, and had a considerable practice in Dublin in the middle of the eighteenth century.