William James Müller, also spelt Muller, was a British landscape and figure painter, the best-known artist of the Bristol School.

The Bristol School is a term applied retrospectively to describe the informal association and works of a group of artists working in Bristol, England, in the early 19th century. It was mainly active in the 1820s, although the origins and influences of the school have been traced over the wider period 1810–40. During the period of his participation in the activities of the Bristol School, Francis Danby developed the atmospheric, poetical style of landscape painting which then initiated his period of great success in London in the 1820s.