John Dyson Heydon KC (born 1 March 1943) is a former Australian judge and barrister who served on the High Court of Australia from 2003 to 2013 and the New South Wales Court of Appeal from 2000 to 2003, and previously served as Dean of the Sydney Law School. He retired from the bench at the constitutionally-mandated age of 70 and went on to chair the Royal Commission into Trade Union Governance and Corruption between 2014 and 2015.