Complex sentence: George Augustus Rochfort (1738--1814), who became the Second Earl of Belvedere in 1774, built Belvedere House, whose interior decoration was carried out by Michael Stapleton, a leading stucco craftsman of his time.
Split into simpler sentences: George Augustus Rochfort (1738--1814), who became the Second Earl of Belvedere in 1774, built Belvedere House. The interior decoration of Belvedere House was carried out by Michael Stapleton, a leading stucco craftsman of his time.