Dr. Robertson was a clergyman, historian, and chancellor of the University of Edinburgh, which commissioned and still owns his portrait by Raeburn of 1792. The younger Robertson studied law and was admitted to the bar as an advocate in 1775. In 1779 he was chosen procurator, or chief counsel, to the Church of Scotland. In 1805 he was seated on the Scottish bench with the title Lord Robertson. He was a judge of the Court of Session, Scotland’s supreme civil court, until 1826 and died nine years later.

http://www.metmuseum.org/works_of_art/collection_database/european_paintings/william_robertson_1753_1835_lord_robertson_sir_henry_raeburn/objectview.aspx?collID=11&OID=110001813