Lieutenant Ralph Clark (30 March 1755 or 1762 – June 1794) was a British officer in the Royal Marines, best known for his diary spanning the early years of British settlement in Australia, including the voyage of the First Fleet. Born in Edinburgh, Scotland, Clark saw service in the American Revolutionary War before volunteering for the voyage to Australia. Arriving in New South Wales in January 1788, he filled a number of roles in the newly established colony, including serving on picket duty, guarding convicts, and on the Criminal Court. Having been temporarily promoted to the rank of first lieutenant, Clark was sent to Norfolk Island aboard HMS Sirius in March 1790, which was subsequently wrecked off the island's coast. After a period on the island, he returned to England aboard HMS Gorgon, arriving in June 1792, and was then posted to the West Indies to fight in the French Revolutionary Wars, dying in a battle off the coast of Hispaniola in June 1794. Clark's diaries, although never intended to be published, provide some of the most personal information about the early convict era in Australia, and are currently held by the State Library of New South Wales.